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moto Gp, torque pulsing and traction


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#101 Canuck

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Posted 20 April 2012 - 00:40

A 60-bite tone wheel provides more than sufficient resolution to identify intermittent cylinder misfires... and is used for just that purpose for OBD on late-model production vehicles.

Can someone give me (us) a practical primer on the hardware and math behind this? Can it reliably determine which cylinder is misfiring as well?

Greg, you noted that it was possible to obtain better-than-0.5 degree accuracy with a similar wheel. Apart from the DFT, what else was required?

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#102 Magoo

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Posted 20 April 2012 - 01:28

Can someone give me (us) a practical primer on the hardware and math behind this? Can it reliably determine which cylinder is misfiring as well?


That is its purpose.

http://delphi.com/pd...010-01-0167.pdf



#103 Magoo

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Posted 20 April 2012 - 02:01

Posted Image

Katech Motus V4 lower end. 90 degree bank angle, 75 degree crank. Fires 0 - 345 - 435 - 630 ATDC. Jim Sracic of Oxford Brookes University did the crank sums, including the twin balance shafts, which aren't terribly necessary in the normal configuration but were baked into the design.

Big bang traction theories played no role in the choice of firing sequence. The Motus people simply wanted to give the engine some character -- a heartbeat.

#104 Magoo

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Posted 20 April 2012 - 02:54

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Kind of rambling off-topic now but along with the firing cadence, an equally interesting feature of the Katech-Motus, to me anyway, is its GDI. I am pretty sure this was the first independent or third-party implementation. The box is a Magnetti Marelli diesel piece while the injectors are Bosch, original app GM EcoTech four.

Here I am holding the injector in approximately its installed position. This relatively shallow angle is known in GDI practice as side injection.



#105 desmo

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Posted 20 April 2012 - 03:32

Seems like a pretty logical application of GDI assuming this will be a relatively low revving engine. I like the pushrod valvetrain for that too. Who cares what the specific output is? There's no artificial displacement limit for this bike to conform to, if you can make a light, fuel efficient engine with the target output the displacement is irrelevant. Any other GDI bike engines currently?

#106 manolis

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Posted 20 April 2012 - 06:24

I wrote most of the following 5-years ago in another forum:

An in-line four (or I-4) four-cycle with cross-plane crankshaft means uneven firing intervals.

Instead of the standard 180 crankshaft degrees interval between successive combustions of the conventional “plane-crankshaft” four in-line, like:

I____I____I____I____I____I____I____I

in the cross-plane the firing intervals are 270 crankshaft degrees, then 180 crankshaft degrees, then 90 crankshaft degrees and then 180 crankshaft degrees, like:

I______I____I__I____I______I____I__I

and the sound from the exhaust reminds something like the “gallop pace”.

Regarding the unbalance of the cross-plane I-4 (by the way, with the balance program at http://www.pattakon....duc/balance.exe you can see graphically and by numbers all these), it is different than the unbalance of the conventional I-4.

Besides the heavy unbalanced 2nd order inertia force, the conventional I-4 has also a heavy 2nd order inertia torque:

Posted Image

(the inertia torque on the block and the inertia torque on the crankshaft are the same).
The short curve is for the cross-plane I-4, for equal stroke, rpm, piston mass etc.

2nd order means that it maximizes and minimizes two times per crankshaft rotation.

An idea for this “heavy inertia force”?
In a typical 1600cc I-4, at the red line the unbalanced inertia force is more than 1 ton, i.e. more than 7 times the total weight of the engine.
In the reasonable question: “and why the engine, under the action of such a strong force, doesn’t leave its place/position?” the answer is simple: “it does” and the engine vibrates, i.e. it moves up and down in the rhythm of the acting force, i.e. if you take a “fast” video of your engine running at 6000 rpm (i.e. at 100 crankshaft rotations per second) you will see the engine going up and down 200 times per second .
The elastic engine mounts isolate these vibrations from the car – or motorcycle- frame.
In the expensive cars they put a pair of counter-rotating 2nd order balance shafts (i.e. they rotate at double crankshaft speed) to create an equal and opposite force and so to cancel the 2nd order unbalance force of the conventional I-4.
With the proper offset (along the cylinder axis) of the two balance shafts, besides the inertia force, it is also counterbalanced the inertia torque on the block of the engine (however, the heavy inertia torque on the crankshaft and on the flywheel cannot be reduced).

What the “heavy inertia torque” means?
At high revs the inertia torque is stronger than the instant torque generated by the expansion of the gas into the cylinder. This actually means that if you take the actual torque that arrives to the flywheel from the crankshaft, it comprises a strong “inertia” part that offers nothing but stress and friction and a useful torque that finally moves the vehicle.
To really understand the meaning of the inertia torque, look it from the energy view point: in a conventional four in line (I-4) with plane crankshaft (i.e. with crankpins at 0, 180, 180 and 0 crankshaft degrees) when the first piston is at the TDC (top dead center) all the four pistons are immovable (their velocity is zero), i.e. their total kinetic energy is zero (kinetic energy: 0.5*m*V*V, where V is the speed of the piston and m is the mass of the piston with the piston rings and the piston pin and the upper part of the connecting rod). After 90 crankshaft degrees, all the four pistons move quickly and have concentrate a strong amount of kinetic energy. At the BDC (i.e. after another 90 crankshaft degrees) the total kinetic energy of the pistons is zero again. I.e. there is a strong “take and return” of mechanical energy between the flywheel and the pistons two times per crank rotation. And this strong inertia torque does not contribute to the vehicle motion. It just stresses the moving parts of the engine and increases the mechanical friction.

The conventional four in line is not so perfect as you used to think.

And what about the cross-plane I-4?

Here the total unbalanced inertia force is zero.

Also the total unbalanced inertia torque is actually zero (i.e. there is no reciprocation of inertia torque between the flywheel and the pistons). I.e. in the rear tire of the Yamaha R1 arrives only useful energy that makes easier the life of the rider (better feeling, drive closer to the limit etc). The clutch can operate without springs.
Just like in the V-4 with 180 degrees crankshaft.

But there is a pure 1st order strong plane inertia moment. By using a 1st order counter-rotating balance shaft (i.e. it rotates with the crankshaft speed at opposite direction) the total unbalanced inertia moment of the engine becomes zero.

That is, with one balance shaft the cross-plane straight four is better, as regards its inertia balancing, than the best V-8 ! and way, way better than the conventional I-4

The only asymmetry that remains is the uneven firing.

For someone who has a V-8 in his car, he can simulate the cross-plane I-4 by removing the ignition and the injection from the one bank of cylinders. That simple.

As for the turbo applications, one can start by seeing how the V-8 deals with this problem. If a turbo can serve successfully one bank of cylinders, like in the picture below (chevy), the same is true for the turbo-charging of the cross-plane four in line.

Posted Image

The drawback of the cross-plane I-4 is the uneven firing and the need for a 1st order balance shaft (which is way easier and involves way less friction than the two 2nd order balance shafts necessary for the balancing of the conventional I-4).
Another drawback is the lower peak power as compared to the flat-crankshaft straight four (with equal intervals between the exhaust pulses, the tuning / breathing is better).


Back to the conventional flat crankshaft I-4:
The clutch passes to the gearbox both, the “working” torque (i.e. that from the combustion-expansion-compression) and the inertia torque (which, at high revs, is several times stronger).
From another viewpoint, the main torque the clutch and the gearbox passes to the wheel is the inertia torque, with the “working” torque passing like “noise” onto the inertia torque! This is the case.
These two torques have the same “main frequency”.
Any attempt to damp the inertia torque, kills a part of the “working torque” too.

A solution is to allow the crankshaft to rotate at slightly variable angular speed (slightly faster at TDC and BDC wherein the pistons stop moving, and slightly slower at middle stroke wherein the four pistons move quickly) while the primary axle of the gearbox rotates at constant angular speed.
If in the primary transmission (from the crankshaft to the clutch) the gear-wheel on the crankshaft is of special design like:

Posted Image

then the flat crankshaft I-4 no longer passes inertia torque to the gearbox, keeping all its rest advantages.

Thanks
Manolis Pattakos

Edited by manolis, 20 April 2012 - 07:37.


#107 gruntguru

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Posted 20 April 2012 - 07:07

Thanks Manolis. At last somebody has given us an estimate of the relative amplitudes of the inertia and combustion torques.

The inertia torque amplitude is of course determined by the ratio of reciprocating vs rotating masses ie a heavier flywheel or lighter pistons will both reduce the inertia torque.

Inertia "torque" is probably not the most appropriate term (as I mentioned in an earlier post) because the result of this "imbalance" is actually best expressed as a speed or KE variation. The amplitude of the resulting torque oscillation will depend on what the engine is connected to - ie the reselience of the drivetrain.



#108 manolis

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Posted 20 April 2012 - 09:21

Gruntguru,

Here is an estimation of the relative amplitudes of the inertia and combustion torques:

The peak “working” torque of an even firing 4 cylinder is about 3 times its mean torque.

Without a turbo, the mean torque of a racing 1000cc is difficult to pass the 12 Kpm (at 18000 rpm it gives 300 bhp), i.e. the peak “working” torque during the expansion is 36 Kpm.

For a 1000cc 4-cylinder motoGP engine, the maximum allowed bore is 81mm, which means 48mm stroke.

The piston of Honda B16A2 VTEC (red line at 8000rpm) is also 81mm in diameter and has a mass of 300 gr.
Its wrist pin is another 100 gr.
The connecting rod is 600 gr.

I.e. the reciprocating mass per cylinder is about 300+100+(600/3)=600 gr.

Lets say the reciprocating mass of the motoGP flat-crankshaft 1000cc I-4 engine is only half, i.e. 300 gr per cylinder.

At 18000 rpm (28.8 m/sec mean piston speed) the inertia torque (balance program at http://www.pattakon....attakonEduc.htm ) is 125 Kpm of 2nd order (by the way, the unbalanced inertia force is 2,5 tons of 2nd order too).

I.e. the clutch receives a “working” torque of 36 Kpm peak, and 125 Kp of inertia torque (i.e. more than 3 times bigger).
Worse even, the "working torque" varies from a small negative value (say -10 Kpm during compression) to its peak positive value (36 Kpm), while the inertia torque varies from -125 Kpm to 125 Kmp, i.e. the "3 times bigger" is too conservative; the "5 times bigger" is more realistic).
That is, the "working torque" passes to the gearbox/wheel like "noise" over the way stronger inertia torque "carrier".


“The inertia torque amplitude is of course determined by the ratio of reciprocating vs rotating masses ie a heavier flywheel or lighter pistons will both reduce the inertia torque.”

No, the inertia torque amplitude is not related to the rotating mass.
I think what you mean is: "the variation of the angular velocity about its mean value is determined by the ratio of reciprocating vs rotating masses".

Instead of increasing the rotating mass (not good in a racing engine: the response to the throttle becomes slower, to change direction becomes more difficult, the weight increases), the true solution is the use of a special gearwheel (like in the last post) on the crankshaft which, besides engaging the crankshaft to the clutch, it also allows the two parts (the crankshaft, at one side, and the gearbox–wheel at the other side) to rotate as they like.

What actually happens now, is that the system is overloaded (friction, fatigue etc) trying to make the crankshaft to rotate at constant angular velocity, which is not necessary.
I can’t see why the bike makers are not using, yet, this solution.

As I know, the cross-plane crankshaft of R1 is neither a recent patent, nor Yamaha's.

Thanks
Manolis Pattakos

Edited by manolis, 20 April 2012 - 09:22.


#109 Magoo

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Posted 20 April 2012 - 10:07

Google Helmut Fath.

#110 Magoo

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Posted 20 April 2012 - 10:19

Seems like a pretty logical application of GDI assuming this will be a relatively low revving engine. I like the pushrod valvetrain for that too. Who cares what the specific output is? There's no artificial displacement limit for this bike to conform to, if you can make a light, fuel efficient engine with the target output the displacement is irrelevant. Any other GDI bike engines currently?


140 lbs, 1.6L, 161 hp at 7800 rpm in conservative NA road tune. A number of interesting applications might come to one's mind, both naturally aspirated and boosted, due to its compact footprint.

Posted Image







#111 Canuck

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Posted 20 April 2012 - 15:57

That is its purpose.

http://delphi.com/pd...010-01-0167.pdf

Thank you.

#112 PhilG

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Posted 20 April 2012 - 18:25

Had a quick skim through this , missed the techy stuff cos its over my head a bit, although i am familiar with race engine build and manufacture , as i work in motorsport .

Anyway, im more interested in this from a riders point of view, as i have experience of racing V twin bikes in screamer and big bang configurations.

From 2007 i have raced an Aprilia SXV Supermoto in various guises from 450 to 550 in various states of tune over its development, and as it came to its peak , the work was more about making usable power, rather than peak numbers, and most importantly, drivability on the side of the tyre , which is where the lap time comes from .

In 2010 we had an MXV 450, which was the motocross based bike, and its engine was in big bang configuration , as opposed to screamer for the SXV, and initial runs showed what the difference instantly... drive. As you open the throttle, in screamer , you have to be very careful when you pick up the throttle because when you are leaned over it will spin up, and if you have good tyres, that usually means a highside is on the way , unless you are fairly talented.. i run Michelin tyres because that is the tyre dictated by the series , which has good ultimate grip, but lets go , as opposed to a dunlop which gives warning and slides earlier , and is more predictable.

In big bang, you can just bang the throttle on and it wont spin up anywhere near as easy, in fact you have to try to make it do it, in the wet its almost like cheating , because the level of grip is far better than offered in screamer mode.. but the trade off is the top speed is not as impressive as screamer , which makes better power as the revs increase.

The upshot is that although the SXV is far faster, it doesnt make a faster lap time , on all but the quickest of tracks because the drive/rideability outweighing the straight line speed advantage.

This is why the flat plane crank of the R1 makes it turn lap times , and be easier on the tyre , because the power pulses allow the tyre recovery time, rather than lighting it up , which in bike racing is the ultimate goal... tyre life .

#113 gruntguru

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Posted 21 April 2012 - 06:35

Manolis.
Thanks for correcting me on inertia torque vs angular speed variation - you are quite correct.

PhilG.
Thanks for your input - great to have the opinion of someone who has actually ridden both types at the limit. Are the "screamer" and "big bang" mechanically identical, ie shared crankpin V twin?

#114 Magoo

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Posted 21 April 2012 - 10:53

This is why the flat plane crank of the R1 makes it turn lap times , and be easier on the tyre , because the power pulses allow the tyre recovery time, rather than lighting it up , which in bike racing is the ultimate goal... tyre life .


I'm sure we're all familiar with the theory. The trouble is there is no particular reason to believe it, especially in regard to the Yamaha R1.

1. Unlike a single (1x per cycle) or a twin (1x per rotation) a 4-stroke four must fire four times per cycle dba 720 degrees of crankshaft rotation. If we examine all the practical phasing possibilities, there is no way to distribute the four firing events to provide a time interval worth talking about. The Yamaha R1 operates at 12,500 rpm, or 416 firing events per second -- equivalent to a V8 running at 6250 rpm. What time interval?

2. There is no evidence that a so-called recovery time between firing impulses is good or bad or makes any difference at all in regard to traction or tire life. Perhaps I am misinformed, but I'm not aware of any reputable tire company that has made such a finding.

For its part, Yamaha makes no such claims for the R1. Its claim is that the crossplane crank provides smoother feedback to the rider, allowing him/her to apply throttle more accurately. That theory has some problems as well, but that's another theory.

#115 PhilG

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Posted 21 April 2012 - 11:08

Manolis.
Thanks for correcting me on inertia torque vs angular speed variation - you are quite correct.

PhilG.
Thanks for your input - great to have the opinion of someone who has actually ridden both types at the limit. Are the "screamer" and "big bang" mechanically identical, ie shared crankpin V twin?



Yes they are , just a case of altering the cam timing , and loading the correct map to suit, maybe an hour's work , ideally you would have two bikes , and have one for wet setting , with big bang and softer suspension settings, but reality is that if you do get two bikes, you need them to be the same , no point in having to ride a wet bike in the dry when you have a problem... we had the luxury of switchable maps , so a lot of work was done on that , to make the power delivery softer to cope with the damp conditions , and muddy tarmac when the dirt gets dragged on to the rest of the track. Knowing that you can calm the power delivery as a screamer to a point where it is as forgiving as a big bang means that the big bang soon gets canned , as the lack of top end is too much.

Also we are using 170 section rear tyres , and looking at rightaround 70 hp , so its not like the bike has too much power for the tyre, but we run very soft compound , and of course the bike is always sliding a lot too.. we worked on always having enough power on hand , without having the rear spin up on hard throttle early in the turn.

This engine now seems to be the unit of choice for formula SAE cars, being light and torquey, as a 550 , but nearly all teams seem toover complicate the job by going to engine management systems that are too complex, instead of piggy-backing on the stock stuff and learning to improve the performance, rather than just getting it to run.

Allsorts of benefits from wasted spark, fuel in on closed throttle, point of injection changes, and fuel mix / ignition advance were all used to get the ultimate balance of power and rideability, the team owner spent hours on the mapping side making allsorts of changes that we validated on the track by laptime , feel and tyre life, not sat in a room doing 100mph standing still.. the results were a bike that flattered me as a rider , and everyone struggled to pass .

With the SXV we saw allsorts of people putting bikes with his maps in , and being improved on paper, but they never went quicker on the track after, and they never lasted as long, which told us everything we needed to know..

Comedy was taking our #001 ecu and fitting it to another bike without telling the rider , and watching him ride from his usual midpack , to the sharp end, in 4 laps , it was enough to convince him that dyno graphs mean nothing at all , if you cant ride what you are getting.



#116 manolis

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Posted 21 April 2012 - 12:52

Yes they are , just a case of altering the cam timing , and loading the correct map to suit, maybe an hour's work , ideally you would have two bikes , and have one for wet setting , with big bang and softer suspension settings, but reality is that if you do get two bikes, you need them to be the same , no point in having to ride a wet bike in the dry when you have a problem...
. . .
Comedy was taking our #001 ecu and fitting it to another bike without telling the rider , and watching him ride from his usual midpack , to the sharp end, in 4 laps , it was enough to convince him that dyno graphs mean nothing at all , if you cant ride what you are getting.


PhilG,

According some drawings from the Internet, the crankshaft of the Aprilia SXV and MXV has a single crankpin (i.e. no crankpin offset).
The following plots (made by the balance program at http://www.pattakon....attakonEduc.htm ) are for different arrangements.
Here is the inertia torque of the SXV 77deg

Posted Image

Here is the comparison of the SXV 77 deg inertia torque to that of a V-90 degrees or a I-2 with crankpins at 0 and 90 degrees (Ducati, last Yamaha TDM):

Posted Image

Here is the inertia torque of an even firing I-2 (crankpins at 0 and 360 degrees, cyan curve) versus a I-2 with crankpins at 0 and 180 degrees:

Posted Image

Here, in the previous plot it has been added, for comparison, the inertia torque of the SXV 77 degrees:

Posted Image

Here, in the previous plot it has been added, for comparison, the inertia torque of the V-90:

Posted Image

The above are for same pistons, same connecting rods, same revs.

The inertia torque of the SXV – MXV is quite small (only a little bigger than a V90 like ducati).

The big bang cannot justify the big difference in traction between the SXV and the MXV you ride.
If the effect of the big bang (which leaves the tire to calm down before the next power pulse) was so decisive, then the four in line would never be able to compete in a race.

The inertia torque of the 1000cc even firing 4-cylinder at 18000 rpm (moto GP) is, for same piston and same stroke, four times stronger (two times because of the two more pistons, and another two times because of the higher revs) than the inertia torque of the I-2/180 deg arrangement at 13000 rpm, which is already 2.5 times stronger than the inertia torque of the SXV-77deg at the same 13000 rpm.
I.e. the even firing I-4 motoGP passes to the rear tire, at 18000 rpm, ten times stronger inertia torque than what your SXV – MXV passes to the rear tire at 13000 rpm, while both engines (I-4 motoGP and SXV – MXV) have actually the same “working” power pulse (combustion-expansion-compression).

What I think is that the big deference between your big bang MXV (combustions at 0 and 77 degrees) and your SXV (combustions at 0 and 283 degrees) comes from the substantially different tuning.
The first has lower, but smoother, torque curve, and linear increase of torque with the throttle position, while the second sacrifices the linear response (like the old two strokes) for the sake of the peak power.
It would be interesting if the MXV engine was tuned to give the peak power of SXV. This would be the correct comparison.

Do you remember the Toyota clone of Honda VTEC? I mean the VVTLi engine of corolla and celica. The torque hole at the middle revs was so deep, that many drivers complaint for dangerous behavior or the car: you press the gas pendal, nothing happens, and suddenly you have all the power on the wheels.
Do you remember the famous Bimota 2-cylinder 500cc 2-stroke Vee project? The response was so un-linear, that a number of bikers killed before phasing out the project and bankrupting. Imagine being leaned at a corner and suddenly the power in the rear wheel doubles, that good.

Similarly, nobody complains about Ducati’s peak power at motoGP. The V-4 arrangement allows as big bang as the MXV, and the inertia torque can be actually zero (with crankpins at 0 and 180 degrees), way smaller than MXV’s with half capacity. However it is difficult for the rider, any rider, to control this power (not even Rossi can handle it) because it comes suddenly.

With a single intake cam lobe for all conditions (dry or wet race, acceleration, top speed, cranking etc) you cannot have it all.
If you need top power, you have to sacrifice the smooth response and the partial load operation. If you want easy handling, you sacrifice peak power.

Now take a look at the desmodromic VVA (DVVA) at http://www.pattakon....ttakonDesmo.htm .
It is like having infinite camshafts in the motorbike, and choose each moment the perfect one.
Look what type of valve lift profiles it can give:

Posted Image

It needs not throttle valves, at all.
If a corner is approaching, the rider selects a valve lift profile like MXV’s or smoother, after the corner he selects a valve lift profile like SXV’s and in the long line it is selected the wilder available for top power.
Without valve springs, with fully and independently variable lift and duration, with rolling – instead of sliding – friction, with lightweight moving parts etc,
imagine what Rossi could do with it in motoGP.

As you write: "dyno graphs mean nothing at all , if you cant ride what you are getting"

The "father" of the DVVA is the VVA-roller version at http://www.pattakon....takonRoller.htm (it is not as variable as the DVVA, and it needs valve restoring springs)
The following plot is the datalog on the road with the Hondata S200 system (prototype car: Honda VTEC B16A2 modified to pattakon VVA roller)
The blue curve is the quantity, per cycle, of air that is handled by the engine. At a first approach the blue curve gives the form of the torque curve.
The red curve gives the form of the power curve.

Posted Image

Did you ever saw a power curve like this?
The DVVA is the evolution of this and can do a lot more.

Thanks
Manolis Pattakos

#117 Magoo

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Posted 21 April 2012 - 16:15

As Desmo astutely noted, the Big Bang legend begins many decades ago in the USA with the Harley-Davidson V-twin in AMA dirt track racing. As the story went, the Harley's loping firing sequence allowed the rear tire to "dig in" to dirt surfaces in some magical way that conventional motorcycle engines couldn't -- thus giving the Harley its long-running lock on race wins and championships.

Right. The Harley's traditional 50 percent displacement advantage under the AMA rules couldn't have had anything to do with it.

Along with its 45-degree vee angle, there is another aspect of the Harley that might be worthy of notice -- namely, the great bleeding pair of cast-iron flywheels more or less necessitated by the historic (don't say archaic) design. I believe the KR/XR flywheel assembly (photos below) weighs in the neighborhood of 21 pounds, which is sort of interesting to reflect upon in that the whole f**king motorcycle weighs 295 lbs with a gallon of gasoline. Thus it is possibly not unreasonable to propose that flywheel inertia might have some noticeable effect on driveline and rear tire behavior. Call it a stab in the dark.

Posted Image

Posted Image






#118 PhilG

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Posted 21 April 2012 - 18:24

PhilG,

According some drawings from the Internet, the crankshaft of the Aprilia SXV and MXV has a single crankpin (i.e. no crankpin offset).
The following plots (made by the balance program at http://www.pattakon....attakonEduc.htm ) are for different arrangements.
Here is the inertia torque of the SXV 77deg





The inertia torque of the SXV – MXV is quite small (only a little bigger than a V90 like ducati).

The big bang cannot justify the big difference in traction between the SXV and the MXV you ride.
If the effect of the big bang (which leaves the tire to calm down before the next power pulse) was so decisive, then the four in line would never be able to compete in a race.

The inertia torque of the 1000cc even firing 4-cylinder at 18000 rpm (moto GP) is, for same piston and same stroke, four times stronger (two times because of the two more pistons, and another two times because of the higher revs) than the inertia torque of the I-2/180 deg arrangement at 13000 rpm, which is already 2.5 times stronger than the inertia torque of the SXV-77deg at the same 13000 rpm.
I.e. the even firing I-4 motoGP passes to the rear tire, at 18000 rpm, ten times stronger inertia torque than what your SXV – MXV passes to the rear tire at 13000 rpm, while both engines (I-4 motoGP and SXV – MXV) have actually the same “working” power pulse (combustion-expansion-compression).

What I think is that the big deference between your big bang MXV (combustions at 0 and 77 degrees) and your SXV (combustions at 0 and 283 degrees) comes from the substantially different tuning.
The first has lower, but smoother, torque curve, and linear increase of torque with the throttle position, while the second sacrifices the linear response (like the old two strokes) for the sake of the peak power.
It would be interesting if the MXV engine was tuned to give the peak power of SXV. This would be the correct comparison.


I think the only thing i can draw from this , without appearing rude , is that this typifies the the gulf between riders and engineers........ i happen to be both , so while i can appreciate the technical aspect on paper, its only paper... we race on a track , and that is where you need to be fast. If you rode both bikes , back to back , you would screw up all your paper and throw it in the bin, which is really my main point...... the big bang motor produces so much bottom end power and no wheelspin , that in the wet , its advantage was huge , even over the single cylinder 450's that make up the majority of the field.. my laptimes were fast enough to qualify me in the front row of the Elite class, and this was down to the power delivery, the track was short and needed no top end at all, the previous week we raced the same bike and set up , in the dry and got eaten on top end , but ran away in the corners.

You can only judge by laptime.. everything else to the rider is circumstantial... i know how hard i can get on the throttle with the given grip, and how the bike behaves relative to those around it, no amount of graphs will change that reality.




#119 Magoo

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Posted 22 April 2012 - 01:33

I think the only thing i can draw from this , without appearing rude , is that this typifies the the gulf between riders and engineers........ i happen to be both , so while i can appreciate the technical aspect on paper, its only paper... we race on a track , and that is where you need to be fast. If you rode both bikes , back to back , you would screw up all your paper and throw it in the bin, which is really my main point...... the big bang motor produces so much bottom end power and no wheelspin , that in the wet , its advantage was huge , even over the single cylinder 450's that make up the majority of the field.. my laptimes were fast enough to qualify me in the front row of the Elite class, and this was down to the power delivery, the track was short and needed no top end at all, the previous week we raced the same bike and set up , in the dry and got eaten on top end , but ran away in the corners.

You can only judge by laptime.. everything else to the rider is circumstantial... i know how hard i can get on the throttle with the given grip, and how the bike behaves relative to those around it, no amount of graphs will change that reality.



What Manolis showed you is that the specific advantage you claimed is not there. It does not exist. If there is a performance benefit in the engine's firing sequence, it's not the one you originally theorized. It has to be something else. You need to devise a new theory.

Now, it's obvious to me that if you have less wheelspin at a particular rpm with your favored combination, it's because a) you now have less torque at that rpm or b) you now have a more manageable torque curve through that rpm. Why go looking for a zebra when there is a plain old horse looking you straight in the eye?

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#120 gruntguru

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Posted 22 April 2012 - 09:06

One thing Manolis didn't give us, is a graph showing the combustion torque of the SXV and the MXV. Since the inertia torque is quite low - especially at the lower revs used for cornering - the big-bang version will produce a halving of the frequency of cyclic torque application to the rear tyre. Comparison with the much higher inertia torque of the 4 cyl bikes is not valid either since that phenomenon occurs at 4 times the frequency of the big-bang.

So I won't race in to write off PhilG's observations - he has one huge advantage over the rest of us. Is it possible that the big-bang frequency of the SXV coincides with the stick-slip frequency of the rear tyre and gives the rider a much larger window for "feel" at the edge of traction?



#121 PhilG

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Posted 22 April 2012 - 12:07

What Manolis showed you is that the specific advantage you claimed is not there. It does not exist. If there is a performance benefit in the engine's firing sequence, it's not the one you originally theorized. It has to be something else. You need to devise a new theory.

Now, it's obvious to me that if you have less wheelspin at a particular rpm with your favored combination, it's because a) you now have less torque at that rpm or b) you now have a more manageable torque curve through that rpm. Why go looking for a zebra when there is a plain old horse looking you straight in the eye?


Well one of us rides and has a British Championship to our name and one doesnt..what i do have is a wealth of experience, having raced for 37 years, in the UK, Europe and the USA, as well as experience of lots of bikes through testing for magazines in recent years....i may not be the fastest any more , but i know the bikes i helped along the way were faster than the factory efforts when they met head to head at World championship level... he can sit at his laptop till the cows come home , he's wrong , i am right.
Maybe i suddenly become more talented dependant on the firing order :drunk:


One thing Manolis didn't give us, is a graph showing the combustion torque of the SXV and the MXV. Since the inertia torque is quite low - especially at the lower revs used for cornering - the big-bang version will produce a halving of the frequency of cyclic torque application to the rear tyre. Comparison with the much higher inertia torque of the 4 cyl bikes is not valid either since that phenomenon occurs at 4 times the frequency of the big-bang.

So I won't race in to write off PhilG's observations - he has one huge advantage over the rest of us. Is it possible that the big-bang frequency of the SXV coincides with the stick-slip frequency of the rear tyre and gives the rider a much larger window for "feel" at the edge of traction?


It is all about feel... bike racing is all about feel.. and that doesnt ever show up on any laptop, simulation , or any other media , apart from the track... that tells you everything you need to know , and unless you get behind the handlebars and you do it yourself , you have zero appreciation of what that means... its like trying to tell someone how to play football when you have never kicked a ball yourself.

i have been involved in projects where millions have been wasted , because drivers and riders wishes have been ignored in the pursuit of laptop perfection, and the annoying thing is that there were enough people involved who did know what the problems were, but didnt have enoiugh letters after their name to be listened to.. this conversation epitomises that.

I have no doubt that data acquisition techniques have allowed analysis of even the smallest change in MotoGP , but it doesnt alter the fact that with all the info in the world, without satisfying the rider , its all worthless, i give you Ducati as a prime example.. instead of making a rolling testbed and working their way physically to a solution, they go away , design something in cyberspace, and then scratch their heads when it dont work... but the computer said it would be fine.





#122 Magoo

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Posted 22 April 2012 - 14:25

Well one of us rides and has a British Championship to our name and one doesnt..what i do have is a wealth of experience, having raced for 37 years, in the UK, Europe and the USA, as well as experience of lots of bikes through testing for magazines in recent years....i may not be the fastest any more , but i know the bikes i helped along the way were faster than the factory efforts when they met head to head at World championship level... he can sit at his laptop till the cows come home , he's wrong , i am right.
Maybe i suddenly become more talented dependant on the firing order :drunk:


Nobody questioned your technical knowledge. Please stop insulting mine by pushing theories that are technically impossible.

I've never said that big bang cannot produce an improvement in lap times. I'm saying that your explanation for said improvement has been proven wrong. If it does work, it can't possibly work in the manner you describe. Manolis demonstrated that the mechanism isn't there.

Some time before you arrived in this discussion, I suggested that the probable key to all of this is in rider input/feedback. This seems rather obvious to me in that human perception/response is invariably the wild card. This thinking is also in complete agreement with the stated position of Yamaha engineer Masao Furusawa regarding the crank phasing of the R1: it cleans up an input signal for the rider's (virtual) throttle feedback loop. It has nothing to do with "tire recovery time" or any of that jazz. In other words, it comes down entirely to "rider feel," as you say yourself.

#123 PhilG

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Posted 22 April 2012 - 16:04

Nobody questioned your technical knowledge. Please stop insulting mine by pushing theories that are technically impossible.

I've never said that big bang cannot produce an improvement in lap times. I'm saying that your explanation for said improvement has been proven wrong. If it does work, it can't possibly work in the manner you describe. Manolis demonstrated that the mechanism isn't there.

Some time before you arrived in this discussion, I suggested that the probable key to all of this is in rider input/feedback. This seems rather obvious to me in that human perception/response is invariably the wild card. This thinking is also in complete agreement with the stated position of Yamaha engineer Masao Furusawa regarding the crank phasing of the R1: it cleans up an input signal for the rider's (virtual) throttle feedback loop. It has nothing to do with "tire recovery time" or any of that jazz. In other words, it comes down entirely to "rider feel," as you say yourself.


I am really struggling here... the logic you are using is like the guy in the store saying he doesnt have what i want , in spite of me being able to point to it on the shelf...... please open your eyes and ears to what is being said here.

Big bang delivers flat power, that starts the instant you open the throttle , and you can crack the throttle on the instant you you come off the brakes, pretty much, and accelerates out of the turn in a linear way, so there is no sudden burst of power, no danger of spinning up . and ulitimately, when grip is hard to come by , it hooks up and stays hooked, screamer doesnt allow you to get on the throttle as early, and certainly not so hard and as you are making mid corner accelration, the rear can and does want to break traction far easier, and as such works the tyre harder ..

So please tell why when riding the same bike , with everything else the same, including the base settings for fuel and ignition which were the same, the only alteration being cam timing, that it performs so differently ... what is the magic thing i am missing???

It appears you are able quite easily to tell me that something i (and pretty much every other rider for that matter) take for granted as fact, doesnt really exist, but you cant tell what it is that actually does ..

Once you open your eyes to things that are 'technically impossible' it will give you a far greater insight into the nuances that make a good bike great , but more importantly a very well funded and designed bike an absolute pile of rubbish..


#124 Magoo

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Posted 22 April 2012 - 16:34

I am really struggling here... the logic you are using is like the guy in the store saying he doesnt have what i want , in spite of me being able to point to it on the shelf...... please open your eyes and ears to what is being said here.

Big bang delivers flat power, that starts the instant you open the throttle , and you can crack the throttle on the instant you you come off the brakes, pretty much, and accelerates out of the turn in a linear way, so there is no sudden burst of power, no danger of spinning up . and ulitimately, when grip is hard to come by , it hooks up and stays hooked, screamer doesnt allow you to get on the throttle as early, and certainly not so hard and as you are making mid corner accelration, the rear can and does want to break traction far easier, and as such works the tyre harder ..

So please tell why when riding the same bike , with everything else the same, including the base settings for fuel and ignition which were the same, the only alteration being cam timing, that it performs so differently ... what is the magic thing i am missing???

It appears you are able quite easily to tell me that something i (and pretty much every other rider for that matter) take for granted as fact, doesnt really exist, but you cant tell what it is that actually does ..

Once you open your eyes to things that are 'technically impossible' it will give you a far greater insight into the nuances that make a good bike great , but more importantly a very well funded and designed bike an absolute pile of rubbish..


You are confusing a couple of different things, namely cylinder phasing and torque curve. You are free to prefer a so-called big-bang engine's output characteristics if you choose and it's perfectly valid, but these are not necessarily due to the engine's cylinder phasing. Firing cadence affects an engine's torque curve only to the extent it allows cylinders to interfere with each other -- tuning resonance for example.

You would need to perform a straight ABBA test that excludes all but one variable: engine firing sequence. Everything else, including engine output curves, needs to be functionally identical. If you can validate a performance improvement at that point, then you are one important step closer to proving your assertion that firing sequence somehow improves traction or whatever. But for the moment you have several properties tangled up.






#125 PhilG

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Posted 22 April 2012 - 16:49

You are confusing a couple of different things, namely cylinder phasing and torque curve. You are free to prefer a so-called big-bang engine's output characteristics if you choose and it's perfectly valid, but these are not necessarily due to the engine's cylinder phasing. Firing cadence affects an engine's torque curve only to the extent it allows cylinders to interfere with each other -- tuning resonance for example.

You would need to perform a straight ABBA test that excludes all but one variable: engine firing sequence. Everything else, including engine output curves, needs to be functionally identical. If you can validate a performance improvement at that point, then you are one important step closer to proving your assertion that firing sequence somehow improves traction or whatever. But for the moment you have several properties tangled up.


Well ok, you must be right, i'll take me trophies back.


#126 John Brundage

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Posted 22 April 2012 - 20:22

I am a bit confused. Big bang and other terms are being used, but what exactly makes the engine big bang? Manolis early was comparing I4 flat plane and cross plane cranks. I was under the impression that the discussions was related to the different impulses and characteristics and how it affects the traction of a bike. I understand how Phil's cam timing will change the characteristics of a engine. But, how are these the same? And, yes, I did go back and read the complete thread.

#127 Magoo

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Posted 22 April 2012 - 21:14

I am a bit confused. Big bang and other terms are being used, but what exactly makes the engine big bang? Manolis early was comparing I4 flat plane and cross plane cranks. I was under the impression that the discussions was related to the different impulses and characteristics and how it affects the traction of a bike. I understand how Phil's cam timing will change the characteristics of a engine. But, how are these the same? And, yes, I did go back and read the complete thread.


That's part of the problem, as I noted earlier in the thread. The term "big bang" itself seems to be infinitely elastic and when a word or phrase can mean almost anything, eventually it comes to mean nothing at all. The discussion quickly devolves into meaningless technobabble.

As I seem to remember it, the "big bang" term was originally applied to a Honda NSR 500 V4 two-stroke in the early 90s that was designed to fire all four cylinders within 75 or 90 degrees of rotation, and Yamaha quickly followed with something similar in concept. "Big bang" then became something of a buzzword and has since broadened in application to include most anything that employs cylinder phasing that might be considered interesting. The terms "screamer" and "long bang" also arose to describe configurations that contrasted with "big bang" in some way. Apparently, a "screamer" is anything that isn't a "big bang." Such as a Detroit Diesel or a Pratt & Whitney Wasp, I suppose.

For example, Aprilia makes a 77 degree V twin in two general configurations that use the same crankshaft phasing but two different firing sequences. One is termed a "big bang" and the other a "screamer" when in reality, neither engine qualifies as either by any rigorous definition. They are merely "big bang" and "screamer' with respect to each other in a relative sort of way. if this sounds more like marketing than engineering, well there we are.

So at this point, the term "big bang" is really no more than a sort of bench term, like "big block" or "small block" or "three-quarter race cam." What does it mean? Whatever you want it to mean. As the lady in the Saturday newspaper column used to say, you are a poet.




#128 John Brundage

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Posted 22 April 2012 - 22:01

Ok, I get it.
Phil, based on Magoo's explanation, how does changing the cam timing change the engine from a 'screamer' to a 'big bang'? I'm not questioning how cam timing can change the characteristics of the engine and the feel of the bike. Your input is insightful and appreciated, but aren't you, as Magoo suggested confusing a couple things?

Now, a little off topic, as I realize the results to the following question has no effect on cylinder phasing, but may affect the feel of the bike.
Can header design be used to alter impulses? i.e., on an I4, would a change from a 4-2-1, to a 4 into 1 or primary tube pairings be used to change feel? Are there any bike engines where header design can affect feel?

#129 PhilG

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Posted 22 April 2012 - 22:41

Ok, I get it.
Phil, based on Magoo's explanation, how does changing the cam timing change the engine from a 'screamer' to a 'big bang'? I'm not questioning how cam timing can change the characteristics of the engine and the feel of the bike. Your input is insightful and appreciated, but aren't you, as Magoo suggested confusing a couple things?

Now, a little off topic, as I realize the results to the following question has no effect on cylinder phasing, but may affect the feel of the bike.
Can header design be used to alter impulses? i.e., on an I4, would a change from a 4-2-1, to a 4 into 1 or primary tube pairings be used to change feel? Are there any bike engines where header design can affect feel?


I dont get what i can be confusing?? One change .. that is all we made.. cam phasing to change from big bang to screamer.

You have to change something with relation to something else.. the MXV has a shared crankpin.. so you wont be doing that in a hurry LOL, so the change is achieved by locking the crank, and then rotating the front cam 180 degrees, by tapping the gear off the taper and then replacing it 180 from where it was.thus rephasing the front cylinder relative to the rear.



The motor comes in big bang, as its an MX bike and the configuration suits off road perfectly , in the way that it allows the bike to grip in a way that you need it to on the dirt , and provide smooth linear power ( but apparently the computer says this doesnt work).. i raced it twice as an MX bike , and apart from the gearing being a bit tall , it was the easiest thing to ride , power wise that i had ever had... and i've had a few bikes in my time.

Whether its not truly big bang is sematics... the manual says big bang , so Aprilia thinks it is , the maps are labelled 'big bang' & 'screamer' , so thats good enough for me.

As for the pipes, yes, it makes a difference to power characteristics, i think motoGP bikes run seperate pipes because they can , as the usual need for a silencer is what drives superbikes to run 4-2-1 or 4-1 .. The MXV stock pipe was 2-1-2 but that was done for packaging.. the factory MXV pipe was two seperate single systems , which cost a bomb, and were very prone to damage, although the team owner bought one we never got to fit it, as the maps were different and we wanted a base to start from.

Edited by PhilG, 22 April 2012 - 22:45.


#130 sherpa

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Posted 22 April 2012 - 23:02

I have been watching this topic for a while, but have resisted posting until I saw PhilG 's post. I couldn't agree more, the distance between 'theory' and practice is quite large and if you dont ride a motorcycle and have not tried to fight for traction with the two different setups it is difficult to actually understand or to put in words why the big bang setup is easier to ride, but it is. I am an engineer as well as a rider and there are some things you just accept and just get on with it, if you want to be competitive. Chassis flex on motorcycles is another thing that works but is difficult to quantify or measure, just accept it. Getting back to the big bang engines- if you take for example a single cylinder two stroke MX bike and a single cylinder four stroke MX bike, the two stroke will be quicker in a straight line but the four stroke is much easier to find traction on, due to the firing pulses being further apart. If a bike breaks traction and starts to wheelspin and you back off the throttle slightly it will regain traction and I personally think this is what is happening with a big bang engine, the power pusles are further apart and to me its like blipping the throttle to gain traction except you dont have to do it the engine configuration is doing it for you. Just my thoughts
Cheers Greg

#131 gruntguru

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Posted 22 April 2012 - 23:07

I am a bit confused. Big bang and other terms are being used, but what exactly makes the engine big bang? Manolis early was comparing I4 flat plane and cross plane cranks. I was under the impression that the discussions was related to the different impulses and characteristics and how it affects the traction of a bike. I understand how Phil's cam timing will change the characteristics of a engine. But, how are these the same? And, yes, I did go back and read the complete thread.

I am not surprised people are confused. For a start, there are two sources of torque fluctuation being discussed.
1. Cylinder pressure. Changing the firing order to produce a big-bang or an extended-bang instead of the usual even spacing. The amplitude of the torque fluctuations is not RPM dependent. The frequency of the torque impulses is every 720 degrees.

2. Inertia torque. Fluctuations in torque due to stop-start motion of reciprocating parts. Very prevalent in single cyl and 4 cyl even-fire engines. Eliminated in the Yamaha cross-plane crankshaft concept. Inertia torque amplitude increases with rpm. The frequency of the torque impuses is every 180 degrees.

So although the Yamaha concept is sometimes referred to as big-bang, the main effect is actually to quieten torque impulses. Interestingly the impulses being quietened are high frequency while the low frequency "cylinder pressure" impulses are made stronger. From PhilG's comments it seems that these low frequency impulses may be important to traction and feel.

Phil, based on Magoo's explanation, how does changing the cam timing change the engine from a 'screamer' to a 'big bang'?

In big-bang configuration the engine fires at 0,77,720 . . . . degrees. In screamer configuration it fires at 0,437,720 . . . . degrees. To make this happen, the camshafts on one cylinder have to be rotated 180 degrees (delaying its cycle by 360 degrees). The spark for that cylinder must also be changed by 360 degrees. The effective "valve timing" is not changed.

Edited by gruntguru, 22 April 2012 - 23:12.


#132 PhilG

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Posted 22 April 2012 - 23:20

I have been watching this topic for a while, but have resisted posting until I saw PhilG 's post. I couldn't agree more, the distance between 'theory' and practice is quite large and if you dont ride a motorcycle and have not tried to fight for traction with the two different setups it is difficult to actually understand or to put in words why the big bang setup is easier to ride, but it is. I am an engineer as well as a rider and there are some things you just accept and just get on with it, if you want to be competitive. Chassis flex on motorcycles is another thing that works but is difficult to quantify or measure, just accept it. Getting back to the big bang engines- if you take for example a single cylinder two stroke MX bike and a single cylinder four stroke MX bike, the two stroke will be quicker in a straight line but the four stroke is much easier to find traction on, due to the firing pulses being further apart. If a bike breaks traction and starts to wheelspin and you back off the throttle slightly it will regain traction and I personally think this is what is happening with a big bang engine, the power pusles are further apart and to me its like blipping the throttle to gain traction except you dont have to do it the engine configuration is doing it for you. Just my thoughts
Cheers Greg


Thank God... an ally... and yes i agree, i have raced two strokes and now have CRF250 as a play bike after a 125 2 stroke.. i think 1 lap on the two bikes is worth 20 years of calculations.. it tells you everything you need to know.

And as for chassis stiffness... thats what you get when car people make bikes LOL... anyone who makes a carbon chassis instantly tells me they are clueless.. i have seen factory kawasaki frames having bits hacked off them so they actually have flex , and watched the entire Ilmor project end up down the pan cos someone who should have known better couldnt make a chassis without a hinge in the middle..

So what do you / have raced/ridden.



#133 Canuck

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Posted 23 April 2012 - 01:41

That is its purpose.

http://delphi.com/pd...010-01-0167.pdf

Does this allow the knock sensor to be disposed of then? I assume that falls under a misfire event though they don't define misfires.

#134 Magoo

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Posted 23 April 2012 - 01:49

if you take for example a single cylinder two stroke MX bike and a single cylinder four stroke MX bike, the two stroke will be quicker in a straight line but the four stroke is much easier to find traction on, due to the firing pulses being further apart.


Old wives' tale, no truth to it. Four strokes tend to have more manageable torque curves, that's all.

#135 Magoo

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Posted 23 April 2012 - 01:53

Does this allow the knock sensor to be disposed of then? I assume that falls under a misfire event though they don't define misfires.


Nope, knock detection is still required. The misfire monitor in OBD is essentially a diagnostic. If it detects a skip it can't really correct it, only initiate an MIL and so forth.


#136 sherpa

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Posted 23 April 2012 - 03:07

Old wives' tale, no truth to it. Four strokes tend to have more manageable torque curves, that's all.

Are you really sure about that statement, so the old 500 2 stroke GP bikes had nice linear power did they!

#137 bigleagueslider

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Posted 23 April 2012 - 03:07

Thank God... an ally... and yes i agree, i have raced two strokes and now have CRF250 as a play bike after a 125 2 stroke.. i think 1 lap on the two bikes is worth 20 years of calculations.. it tells you everything you need to know.

And as for chassis stiffness... thats what you get when car people make bikes LOL... anyone who makes a carbon chassis instantly tells me they are clueless.. i have seen factory kawasaki frames having bits hacked off them so they actually have flex , and watched the entire Ilmor project end up down the pan cos someone who should have known better couldnt make a chassis without a hinge in the middle..

So what do you / have raced/ridden.


PhilG,

Your point about the differences of opinion between engineers and riders/drivers is one that has existed as long as there has been motor racing. Before the advent of data acquisition and telemetry, the engineers had to rely on the word of the rider/driver. But now that we have sophisticated data acquisition systems and computer simulation softwares, the engineers and designers know just how a bike or car will perform on a particular track even before it turns a lap.

With bike road racing, the skills of the individual rider are still a bigger factor than those of the driver of a road race car, due to the fact that bike racing requires much more physical input from the rider.

slider


#138 manolis

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Posted 23 April 2012 - 06:54

In big bang, you can just bang the throttle on and it wont spin up anywhere near as easy, in fact you have to try to make it do it, in the wet its almost like cheating , because the level of grip is far better than offered in screamer mode.. but the trade off is the top speed is not as impressive as screamer , which makes better power as the revs increase. (post 112) PhilG

So the screamer has more power (and more peaky torque, and un-linear power delivery), while the big bang’s power is more manageable.
If you decrease SXV’s power to be as much as MXV’s, is the difference that much?


Comedy was taking our #001 ecu and fitting it to another bike without telling the rider , and watching him ride from his usual midpack , to the sharp end, in 4 laps , it was enough to convince him that dyno graphs mean nothing at all , if you cant ride what you are getting. (post 115) PhilG

By the ECU reprogramming / re-mapping you cannot affect the configuration of the camshafts (the engine remains big bang, if it were big bang before, or screamer, if it were screamer before).
So, with the same timing of camshafts relative to the crankshaft and a different ECU programming, you can cause a great change in the times of the rider.
The same thing I say in my posts: more important than the peak power is the linear response and the easy control of the engine.
Our difference is that you insist that this is caused mainly by the big bang arrangement, while I support that the effect of the big bang is not comparable to the effect of a Variable Valve Actuation system like the pattakon DVVA http://www.pattakon....ttakonDesmo.htm , which enables top peak power and at the same time top bottom end power and linear response.
A characteristic of the Honda Civic VVA-roller prototype car at http://www.pattakon....attakonVtec.htm (look the available valve lift profiles as compared to the original ones): it proved boring as compared to the slower original VTEC 1600cc 160 bhp, because the second has quite un-linear torque delivery: the driver feels it goes faster, but the timer / clock says the opposite.


the big bang motor produces so much bottom end power and no wheelspin , that in the wet , its advantage was huge , even over the single cylinder 450's that make up the majority of the field.. (post 118) PhilG

The “big bang” cannot significantly affect the “bottom end power”. But if you decrease the peak power, it is easy to have more “bottom end power”.
Think: if with the DVVA on the cylinder head of you MXV you choose a way softer “valve lift profile” (say half valve lift, no overlap at all, less duration) than your current MXV, the bottom end power is improved, as well as the drivability of the engine on a slippery race.
At the limit, imagine a race with slippery mad on it. A 20 bhp MXV with “more bottom end power” wins a 50 or 70 bhp MXV.


Big bang delivers flat power, that starts the instant you open the throttle , and you can crack the throttle on the instant you you come off the brakes, pretty much, and accelerates out of the turn in a linear way, so there is no sudden burst of power, no danger of spinning up . and ulitimately, when grip is hard to come by , it hooks up and stays hooked, screamer doesnt allow you to get on the throttle as early, and certainly not so hard and as you are making mid corner accelration, the rear can and does want to break traction far easier, and as such works the tyre harder .. (post 123) PhilG

The tuning, and not the big bang, delivers the "flat power".
The big bang makes the power more "manageable". The question is "how much?"

For same peak power, the difference between the big bang and the screamer configuration - in practice and according world champions, is not that big:

In motoGP you cannot “play” with the peak power. If you sacrify a good part of the peak power for the sake of the "smooth power delivery", you lose.

Ducati’s motoGP crankshaft is 0-0-360-360 degrees.

In the big bang configuration it is very similar to your MXV (90 degrees instead of 77, simultaneous ignition in pairs of cylinders at 0 and 90 crank degrees, then at 720 and 810 crank degrees, and so on). Both leave for about the same crank degrees (630 for Ducati, 643 for MXV) the rear tire to calm down before the next power pulse.

In the screamer configuration the ignition sequence is 0, 90, 360, 450 crankshaft degrees, which is way worse than your SXV configuration wherein only two power pulses happen per two crank rotations: at 0 and 283 degrees.
Ducati screamer leaves – at most – 270 crank degrees to the rear tire to calm down before the next power pulse, while SXV leaves 437 degrees (almost double).

According your theory, the difference between the big bang and the screamer configuration of Ducati motoGP has to more than noticeable (it has to be bigger than the difference between your MXV and the SXV, according the previous analysis).

Quote from the Internet:

Hayden “leaning towards big bang” (Nov 11, 2010):
“That's it – the season is finally over!” said Hayden on Wednesday evening. “Today was a positive day for us. We tried the screamer and it wasn't easy to switch between engines but it was important to do a proper test on them both and get the data we need to make an important decision. I am leaning towards sticking with the big bang but we will make the decision together.

According Hayden, the difference is not significant.

Thanks
Manolis Pattakos

#139 PhilG

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Posted 23 April 2012 - 07:14

Old wives' tale, no truth to it. Four strokes tend to have more manageable torque curves, that's all.



So what you are saying , is that assuming equal capacity , there is no difference in the performance of the two then , as far as top speed is concerned. :lol:

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#140 Magoo

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Posted 23 April 2012 - 08:17

So what you are saying , is that assuming equal capacity , there is no difference in the performance of the two then , as far as top speed is concerned. :lol:


No, that is not what I said. Now you are deliberately trying to be a jackass. Is that really what you want to achieve?

All else being equal, the dinger will make considerably more power. Or, why sanctioning bodies have allowed four-strokes such a huge displacement advantage. For example, the AMA's 250 two-strokes vs. 450 four-strokes. But if you have, say, two 250 MXers, the four-stroke will be slower -- one more reason its throttle is easier to manage.

Below is a review comparison of KTM two-stroke vs. four-stroke MXers. Differences above are discussed as well as some other issues including weight. But you won't find any mention of the two-vs-four stroke traction theory. Want to know why? Because among motorcycle authorities, there is no such theory. It doesn't exist. It's a myth.

http://motocrossacti...S-201-8417.aspx

Same comparo with Yamahas:

http://motocrossacti...T-YAM-7117.aspx

#141 PhilG

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Posted 23 April 2012 - 09:33

Below is a review comparison of KTM two-stroke vs. four-stroke MXers. Differences above are discussed as well as some other issues including weight. But you won't find any mention of the two-vs-four stroke traction theory. Want to know why? Because among motorcycle authorities, there is no such theory. It doesn't exist. It's a myth.


Only amongst those that dont ride ..

Power delivery & traction is everything in bike racing , and yet you dismiss that there are any differences... you say it doesnt exist, but you can watch it, see it and feel it... so tell me what does exist instead of what doesnt , and i might be inclined to take you more seriously.

#142 PhilG

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Posted 23 April 2012 - 11:45

In big bang, you can just bang the throttle on and it wont spin up anywhere near as easy, in fact you have to try to make it do it, in the wet its almost like cheating , because the level of grip is far better than offered in screamer mode.. but the trade off is the top speed is not as impressive as screamer , which makes better power as the revs increase. (post 112) PhilG

So the screamer has more power (and more peaky torque, and un-linear power delivery), while the big bang’s power is more manageable.
If you decrease SXV’s power to be as much as MXV’s, is the difference that much?

THE POWER OF BOTH BIKES HAS TO BE THE SAME , SEEING AS YOU HAVE TWO CYLINDERS USING THE SAME BASIC MAP..
Comedy was taking our #001 ecu and fitting it to another bike without telling the rider , and watching him ride from his usual midpack , to the sharp end, in 4 laps , it was enough to convince him that dyno graphs mean nothing at all , if you cant ride what you are getting. (post 115) PhilG

By the ECU reprogramming / re-mapping you cannot affect the configuration of the camshafts (the engine remains big bang, if it were big bang before, or screamer, if it were screamer before).
YES I AGREE, THIS WAS PURELY A SCREAMER MAP UPDATE, WHICH LOTS OF CHANGES FROM THE ONE HE HAD

the big bang motor produces so much bottom end power and no wheelspin , that in the wet , its advantage was huge , even over the single cylinder 450's that make up the majority of the field.. (post 118) PhilG

The “big bang” cannot significantly affect the “bottom end power”. But if you decrease the peak power, it is easy to have more “bottom end power”.
Think: if with the DVVA on the cylinder head of you MXV you choose a way softer “valve lift profile” (say half valve lift, no overlap at all, less duration) than your current MXV, the bottom end power is improved, as well as the drivability of the engine on a slippery race.
At the limit, imagine a race with slippery mad on it. A 20 bhp MXV with “more bottom end power” wins a 50 or 70 bhp MXV.

YOU MISS THE POINT, WE DONT WANT TO CHANNGE THE CAMS TO TAKE AWAY POWER, THAT IS POINTLESS

Big bang delivers flat power, that starts the instant you open the throttle , and you can crack the throttle on the instant you you come off the brakes, pretty much, and accelerates out of the turn in a linear way, so there is no sudden burst of power, no danger of spinning up . and ulitimately, when grip is hard to come by , it hooks up and stays hooked, screamer doesnt allow you to get on the throttle as early, and certainly not so hard and as you are making mid corner accelration, the rear can and does want to break traction far easier, and as such works the tyre harder .. (post 123) PhilG

The tuning, and not the big bang, delivers the "flat power".
The big bang makes the power more "manageable". The question is "how much?"
THE MAP IS THE SAME FOR BOTH APART FROM THE TIMING

For same peak power, the difference between the big bang and the screamer configuration - in practice and according world champions, is not that big:

In motoGP you cannot “play” with the peak power. If you sacrify a good part of the peak power for the sake of the "smooth power delivery", you lose.

Ducati’s motoGP crankshaft is 0-0-360-360 degrees.

In the big bang configuration it is very similar to your MXV (90 degrees instead of 77, simultaneous ignition in pairs of cylinders at 0 and 90 crank degrees, then at 720 and 810 crank degrees, and so on). Both leave for about the same crank degrees (630 for Ducati, 643 for MXV) the rear tire to calm down before the next power pulse.

In the screamer configuration the ignition sequence is 0, 90, 360, 450 crankshaft degrees, which is way worse than your SXV configuration wherein only two power pulses happen per two crank rotations: at 0 and 283 degrees.
Ducati screamer leaves – at most – 270 crank degrees to the rear tire to calm down before the next power pulse, while SXV leaves 437 degrees (almost double).

According your theory, the difference between the big bang and the screamer configuration of Ducati motoGP has to more than noticeable (it has to be bigger than the difference between your MXV and the SXV, according the previous analysis).

Quote from the Internet:

Hayden “leaning towards big bang” (Nov 11, 2010):
“That's it – the season is finally over!” said Hayden on Wednesday evening. “Today was a positive day for us. We tried the screamer and it wasn't easy to switch between engines but it was important to do a proper test on them both and get the data we need to make an important decision. I am leaning towards sticking with the big bang but we will make the decision together.

According Hayden, the difference is not significant.

Thanks
Manolis Pattakos


where did he say that ?? to me , he is leaning to the big bang because it is easier to ride and make a laptime.. the Ducati has never been short of straight line speed, but it does struggle with laptimes.. why do you think that is.

#143 manolis

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Posted 23 April 2012 - 13:30

where did he say that ?? to me , he is leaning to the big bang because it is easier to ride and make a laptime.. the Ducati has never been short of straight line speed, but it does struggle with laptimes.. why do you think that is.


"Where did he say that ??" PhilG

Search Internet for:
Ducati and “I am leaning towards sticking with the big bang”
You will find it at several different sites / magazines.

When Hayden / motoGP Ducati says:

"We tried the screamer […] to do a proper test on them both and get the data we need to make an important decision.
I am leaning towards sticking with the big bang but we will make the decision together."

what Hayden actually says is:

"the difference between the big bang and the screamer is small, if any".

Hayden prefers the big bang, but the screamer is OK for him, too. The laptimes will be similar. Otherwise his choice should "clearly" be the big bang.

As was expained in my last post, if the big bang MXV is X% better than the screamer SXV (for the same peak power), this difference doubles between the big bang Ducati V-4 motoGP and the screamer Ducati V-4 motoGP, because the last leaves way less time than the SXV to the rear tire to calm down.

I am not saying that the big bang arrangement is worse than the screamer.
What I am saying is that the difference is not as decisive as you insist.

As for the differences the DVVA brings to the engine, they are way more significant than the ignition timing (big bang oor screamer). With the DVVA the engine combines top peak power, top bottom end power, linear response and much more.
By rotating the "valve duration" control shaft and then the the "valve lift" control shaft of the DVVA during the race, it is like replacing the camshafts by others that better match the instant conditions.
And if you like to combine the DVVA with the big bang, it is OK.

Thanks
Manolis Pattakos

#144 sherpa

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Posted 23 April 2012 - 13:38

PhilG,

Your point about the differences of opinion between engineers and riders/drivers is one that has existed as long as there has been motor racing. Before the advent of data acquisition and telemetry, the engineers had to rely on the word of the rider/driver. But now that we have sophisticated data acquisition systems and computer simulation softwares, the engineers and designers know just how a bike or car will perform on a particular track even before it turns a lap.

With bike road racing, the skills of the individual rider are still a bigger factor than those of the driver of a road race car, due to the fact that bike racing requires much more physical input from the rider.

slider


Maybe you should contact Jeremy Burgess and Valentino Rossi as I am sure they have not found that to be the case

#145 PhilG

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Posted 23 April 2012 - 18:45

I am not saying that the big bang arrangement is worse than the screamer.
What I am saying is that the difference is not as decisive as you insist.




Thanks
Manolis Pattakos


What i am saying , is that whatever way you stack the numbers up, and i appreciate the level of knowledge that takes, they are just numbers.. in some instances they are the empirical data , that cannot be questioned, in others , they are just plain wide of the mark.

Things to do with valves, cams and all of that type of stuff can be calculated to the nth degree because it is simple maths... not to me .. but to you number crunching types its able to be done.. way over my head, i just want to know 'is it faster'... however , as we have seen with tuners, we have seen engines where the heads have been worked on , and we are stunned that people take material out , where we would be putting it in .. everyone has there ideas.

When you are trying to get a tyre to work , the key , whether its front or rear, is confidence .. no front feel is what is killing Rossi right now, but what he has has been through god know how many simulators , but it dont work... with the rear you have more input and unless you have been through the whole scenario of finding the limit of grip , and then making changes that affect that.. the Big Bang motor characteristics suit tight tracks where the bike is leaned over a lot , because it doesnt spin the tyre away from under you , and you can be agressive in a way that a screamer doesnt allow, unless you have had a bike spit you off and put you on your arse, you cant begin to comprehend the difference between the the two.

MotoGP is different to what we do , because you dont get on the throttle as hard , because you have 200hp with traction control , the differences are nullified ton a certain extent , but its still enough to make a rider plump for feel and security over straight line speed.



#146 Wolf

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Posted 23 April 2012 - 19:47

I beg to differ from PhilG's and Sherpa's opinions that it has anything to do with riding a bike or not- I mean, we're discussing what made big-bang 500cc bikes successful almost 30 years after the fact and can't with certainty say "it was this or that". Same with Yamaha's cross-plane I4- we can pinpoint what was better than flat-plane (the vid linked highlighted all the benefits, making it look like the best thing since sliced bread), but can we say why the project was dropped like hot potato after a year or two in favour of flat-plane? It's not about riding or not riding- it's about making our assumptions fit the facts, rather than vice versa*. BTW I seriously doubt there is a program which can simulate everything so that it can spit up laptimes and somesuch- if there is, there's a world full of F1 and motorcycle engineers who are using it wrong (how else then to account that racing cars and bikes get faster year in and year out; or even more alarmingly a team like Mercedes taking 3 races to sort out tyre temperature issues, when such program would tell them they'd be running too hoot or too cool)...

I'm glad PhilG has posted, because it gives us his experiences and observations to fit our theories to. Someone might disagree on the interpretation of why is something happening the way it is, but I would think it foolish not to take them under serious consideration because they don't fit our view. Until I spoke with someone 'in the know', I didn't know that one can make bike chassis too stiff (that it's desirable to incorporate lateral flex), or that lowering CoG might adversely affect the handling...

* let's take that Hayden statement for example- what do we conclude about the difference between engines? He did say that "it wasn't easy to switch between engines", and I would lean towards concluding that he spoke as a rider and found it difficult to adapt to quite different driving style necessitated by those two engine configurations. As a someone who has never ridden a motorcycle (am bit of an 'armchair expert' on the subject, haha) I would guess that those differences are not as small as where he brakes or opens the throttle, but different riding style altogether (furthermore, I would risk making a fool of myself, being an 'armchair expert', speculating that different power/torque characteristics would not only affect his line through the corner, because of different composite slip angle/throttle steering, but might also require different way of handling the bike to position it and make it 'stand up' on corner exit).

GruntGuru, I'll have to stick to my using of 'inertia torque', since I believe it most accurately (in terms of 'physical origin' and 'end effect') describes that phenomenon. Inertial forces we're discussing are inertia of parts moving in oscillating straight line movement, which are then transfered to crankshaft by exactly the same means as force created by cylinder pressure (i.e. conrods), creating torque. Speed or KE variations are dependent on things outside this phenomenon- e.g. if you attach a bigger flywheel on exactly the same engine, the 'inertia torque', as we've considered it, will remain exactly the same, but both speed and KE variations will drop. It would IMHO be same error as trying to replace 'force' with 'speed or KE variation'.

#147 gruntguru

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Posted 23 April 2012 - 21:59

GruntGuru, I'll have to stick to my using of 'inertia torque', since I believe it most accurately (in terms of 'physical origin' and 'end effect') describes that phenomenon. Inertial forces we're discussing are inertia of parts moving in oscillating straight line movement, which are then transfered to crankshaft by exactly the same means as force created by cylinder pressure (i.e. conrods), creating torque. Speed or KE variations are dependent on things outside this phenomenon- e.g. if you attach a bigger flywheel on exactly the same engine, the 'inertia torque', as we've considered it, will remain exactly the same, but both speed and KE variations will drop. It would IMHO be same error as trying to replace 'force' with 'speed or KE variation'.

Yes, I am seing it that way now too.

Those who dismiss PhilG are not giving him enough credit. He sounds capable of knowing the difference between extra traction attributable to lower torque availability or a flatter torque curve vs "torque pulsing" or some other unexplained phenomenon.

#148 PhilG

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Posted 23 April 2012 - 22:42

The benefit i have is that i dont have to care about the maths of it all...... i just experience the results.. it would be easy to calculate the experience of jumping out of a plane and reaching terminal velocity, but its absolutely nothing like what actually doing it is like..

When you are racing close, it tells you more than riding alone, and riding alone tells you more than running on a dyno, you can tell the difference between hanging on to someone and having to wait for them to get out of the way before you can open the throttle... the difference is huge when you have the ability to start making a move in the middle of the turn to generate a pass going into the next turn.

this is the bike in action, i'm the guy directly in front of the camera bike off the start.. the guy filming is 16 , im 46 , and he rides at european championship level and the bike is the best 450 Honda i have ever ridden

This is what im on about

Also he is 62 kg and im 102....... in the wet ive been on the front row of these races... thats with a screamer and a wet map, but its nothing like as good as big bang.

He cuts a few laps out, but i ran out of front tyre and couldnt push into the turns. Any advantage is soon seen , believe me.

#149 manolis

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Posted 24 April 2012 - 05:41

PhilG,

My last posts were written under the light of your own posts: a champion who describes his “big bag vs screamer” experience and feeling, after several years of racing.
According your posts, it was much easier for you to ride a big bang MXV with less power, than a screamer SXV.
Your experience is precious.
But your experience does not, necessarily, explain “why”.

What I did was to calculate / approximate the inertia torques of various engine arrangements used in racing motorcycles.
This is pure, and quite simple, mathematics: after a few basic assumptions, I finished with a number of curves that (without being absolutely correct) help in understanding a little more what happens inside the engine, in the gearbox, on the contact of the tire with the road, in the clutch etc.
I deliberately kept away from the calculation of the working (combustion) torque.

Another champion, this time from motoGP, had a different opinion than you. Evaluating his big bang Ducati (a quite similar architecture to your MXV) versus his screamer Ducati (“more screamer” than your SXV screamer), the difference for him was small, if any. He used to ride the big bang (i.e. he was familiar with the big bang), then he made a number of rounds with the screamer in order to evaluate which is the better: “I am leaning on sticking towards the big bang, but . . .”

As I understand it, the worse “traction” screamer SXV needs more power in order to follow the big bang MXV.
More power for the screamer means more “peaky torque” and less linear response to the throttle, which worsens even more its traction control.
Is it so?

And why Rossi cannot compete, with his “big-bang top-peak-power” Ducati?
Is it because of the peaky torque and of the un-linear response of his engine?
What if his engine, maintaining the current peak power, turns to a way smoother and true linear one?
Wouldn’t it be better for Rossi (who has the money) , instead of blaming Ducati for the poor results, to make his own engine / team, like Brawn in F1?

In comparison, Lorenzo keeps wining with his R1 Yamaha that is anything but “big bang”.

It would help if you could evaluate, with your long experience, what percentage of the improvement is caused by the big bang arrangement, and what by the different tuning.

Thanks
Manolis Pattakos

#150 PhilG

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Posted 24 April 2012 - 07:10

PhilG,

And why Rossi cannot compete, with his “big-bang top-peak-power” Ducati?
Is it because of the peaky torque and of the un-linear response of his engine?
What if his engine, maintaining the current peak power, turns to a way smoother and true linear one?
Wouldn’t it be better for Rossi (who has the money) , instead of blaming Ducati for the poor results, to make his own engine / team, like Brawn in F1?

In comparison, Lorenzo keeps wining with his R1 Yamaha that is anything but “big bang”.

It would help if you could evaluate, with your long experience, what percentage of the improvement is caused by the big bang arrangement, and what by the different tuning.

Thanks
Manolis Pattakos


Rossi cannot compete because the chassis is rubbish...

And MotoGP has a totally different set of parameters to what i do, and has traction control which nullifies the main advantage of one over the other ... almost.. that makes it a very different set of problems... with no traction control i think you would find a lot more effort going into big bang.

AND THERE IS NO TUNING DIFFERENCE IN THE TUNING.. the fuel goes in and gets lit , just as it does for screamer... the only difference in the map is when that happens relative to crank phasing.