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moto Gp, torque pulsing and traction


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#151 sherpa

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Posted 24 April 2012 - 07:44

Phil is correct the Moto GP bikes rely heavily on traction control to get grip. This is not that obvious when you are watcing on TV or are at the race live, but if you go and watch the practice days you can really hear the traction control on the bikes as they reach their limits, as there are less bikes on track as each rider is trying to get traffic free laps in. I am sure the engineers would have completely different traction control settings for each configuration, the net result being not a lot of difference in lap times. By the way I dont think Hayden is the best example to pick as two years ago I watched both him and Stoner for the three days at Philip Island and to be honest Hayden was not in the same league. Stoner was basically on the limit every corner of every session, unbelievable to see.It would be interesting to see what setup they would use without traction control.

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#152 Magoo

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Posted 24 April 2012 - 08:50

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.


That is beyond preposterous. The world's great motorcycle manufacturers, tire companies, and racing teams, using the most powerful data acquisition tools available, are unable to validate the existence of this magical property.

And this fellow can feel it in the seat of his pants on his club piddler.

Right.

There is no mystery here. This is simple. Dyno the two engine combinations and lay the plots over each other. Then you will know with metaphysical certainty why one engine exhibits less wheelspin at a given rpm. It has less torque at that rpm.

#153 Magoo

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Posted 24 April 2012 - 09:50

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.


Of course power delivery and traction are critical in motorcycles. Obviously. Nobody ever said otherwise. I'm only saying that some theories about it are Harry Potter stories.

Let's start here, with the hypothesis that a tire benefits in some way through manipulating the intervals between driving impulses in the millisecond range, allowing the tread to "recover" or "calm down" or whatever it is supposed to do, generating more longitudinal grip. How would that work? What is the mechanism by which this occurs?

Does it cool or heat the tire in some instantaneous fashion? Does it increase or reduce the tire's kinetic energy on a macro or micro scale? Does it alter the tire's physical texture or molecular architecture or chemical composition in some way? Am I omitting any possibilities? The theory wouldn't happen to involve time travel or parallel universes, would it?



#154 PhilG

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Posted 24 April 2012 - 11:10

Here is the test of the bike by Dirt Rider Magazine

Here

The email is at the bottom so you can tell them why they are wrong too...

#155 Wolf

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Posted 24 April 2012 - 11:33

Magoo, I've posted earlier how I tried to explain to myself 'common wisdom' of big-bang engines, and I dare say that those millisecond range intervals translate to very tangible distances along tyre circumference (my estimation, without going into much details was if V4 two-stroke was revving at 9000rpm and bike traveling at 180kph, a screamer would have a 'torque spike' every 80mm along tyre circumference... assuming bangbang---bangbang--- configuration, the amount of heat would double but so would the distance between the pulses). Depending on the contact patch length, that difference could amount to having two smaller pulses within the contact patch (heating the tyre almost uniformly, causing the heat to reach deeper into the tyre) or one bigger pulse but the exposed part of the rubber very soon being in the airstream to cool off. If I was to try to devise an experiment to verify that assumption, maybe I would see how the tyre heats up while spinning over a heat source and then comparing it to the tyre spinning over the source producing twice as much heat but with additional oscillations moving it away from heat source (while assuring the same amount of heat was fed to the tyre). *shrug* (this was based on old tyre carcass vs. outmost layer being heated up)

And I think that keyword here would not thee longitudinal, but lateral grip- as applied torque will affect lateral grip in corners. So one as well might take into account tyre relaxation lengths and whatnot (of which I know a diddly squat), or the way that rubber migrates through the contact patch... It's all black art to me, but I am not willing to say that increasing the distance between power pulses from 80 to 160mm will be completely irrelevant (and I've even not considered four-strokes with power pulses spaced at twice the intervals of two-stroke, albeit with smaller amplitude).


As for this part: "That is beyond preposterous. The world's great motorcycle manufacturers, tire companies, and racing teams, using the most powerful data acquisition tools available, are unable to validate the existence of this magical property." Do we know they were trying to validate it? Why would they throw money and resources trying to isolate one single aspect of bike performance, relevant only to some esoteric aspect of racing, when they have some of the best riders in the world giving them feedback on what seems to work better or not? What theories they may or may not devise in the process are almost irrelevant- especially since the ultimate judge in the whole process is the stopwatch; not us who sit and judge what they might've said, or what laptimes a simulator might spit out, just stopwatch... It reminds me of a book on stability of vehicles I once saw- it was full of formulas and lyapunov definitions or whatnot, and was supposed to have answer for everything, but I don't recall ever being mentioned that there is something quite opposite to the stability, and that it was not entirely undesirable.

#156 Tony Matthews

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Posted 24 April 2012 - 11:39

The engine can be set up to run in two configurations-the standard "Big Bang," firing the cylinders in a more closed firing gap (less degrees between ignition), or you can retime the cams and activate another ignition and FI mapping to set the motor in the "Screamer" setting-running like you'd expect a standard twin.

The pistons reach TDC at the same time, regardless of anything else, so how does altering the cam timing and ignition to alter the firing intervals by more than a few degrees change it from Big Bang to Screamer?


It is linear, smooth and explosive all in one.

I know an oxymoron when I see one...



#157 Catalina Park

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Posted 24 April 2012 - 11:50

I know an oxymoron when I see one...




#158 Tony Matthews

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Posted 24 April 2012 - 12:00

:lol: Yeah, that too!

#159 PhilG

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Posted 24 April 2012 - 12:02

The pistons reach TDC at the same time, regardless of anything else, so how does altering the cam timing and ignition to alter the firing intervals by more than a few degrees change it from Big Bang to Screamer?


The bike in question is a V twin so they dont.

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#160 Wolf

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Posted 24 April 2012 - 12:08

The pistons reach TDC at the same time, regardless of anything else, so how does altering the cam timing and ignition to alter the firing intervals by more than a few degrees change it from Big Bang to Screamer?


Tony, it's a four stroke- so by altering those things you change in which stroke is the cylinder in question. Say you rotate the camshaft by 180°, this cylinder will go from end of exhaust while being at TDC to being in peak compression while being at TDC- this way you can move firing pulses from being fairly evenly spaced to being closely spaced. Even more simple example would be the car I drive with inline 2 engine- it has two cylinders firing evenly spaced, but if I was to change valve timing only on one cylinder in the same manner (I don't have to worry about ignition because it has no distributor, and engine mapping because it has carbs) I can make it pure big-bang engine with both cylinders firing at the same time.


#161 gruntguru

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Posted 24 April 2012 - 12:24

That is beyond preposterous. The world's great motorcycle manufacturers, tire companies, and racing teams, using the most powerful data acquisition tools available, are unable to validate the existence of this magical property.

- yet spent large sums pursuing (a whim?) - in the pinnacle of bike racing no less. Beyond preposterous.

#162 sherpa

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Posted 24 April 2012 - 13:24

An interesting insight into Casey Stoner and Moto GP

http://motomatters.c...lide_a_mot.html


http://motomatters.c...ng_fast_em.html


http://motomatters.c..._crucial_c.html

#163 Tony Matthews

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Posted 24 April 2012 - 13:34

The bike in question is a V twin so they dont.

Don't what?

#164 Tony Matthews

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Posted 24 April 2012 - 13:37

Tony, it's a four stroke- so by altering those things you change in which stroke is the cylinder in question. Say you rotate the camshaft by 180°, this cylinder will go from end of exhaust while being at TDC to being in peak compression while being at TDC- this way you can move firing pulses from being fairly evenly spaced to being closely spaced. Even more simple example would be the car I drive with inline 2 engine- it has two cylinders firing evenly spaced, but if I was to change valve timing only on one cylinder in the same manner (I don't have to worry about ignition because it has no distributor, and engine mapping because it has carbs) I can make it pure big-bang engine with both cylinders firing at the same time.

Thanks, Wolf, I'm with you. Which makes me realise that PhilG misunderstood mt comment - I meant that both pistons reach TDC at the same time either as a BB or Scrmr, not simultaneously.

#165 PhilG

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Posted 24 April 2012 - 14:39

Thanks, Wolf, I'm with you. Which makes me realise that PhilG misunderstood mt comment - I meant that both pistons reach TDC at the same time either as a BB or Scrmr, not simultaneously.


Yes LOL... i did , obviously the difference is what stroke they are on .. its been a long day already

#166 desmo

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Posted 24 April 2012 - 15:33

This argument is an ancient one. Back in the era of British vertical twins, some dirtrackers tried setting up their 360 degree (I called them 0 degree but it never caught on) crank engines to fire both cylinders simultaneously to try to mimic the uneven phasing of the H-Ds. It apparently didn't help.

#167 Magoo

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Posted 25 April 2012 - 01:46

- yet spent large sums pursuing (a whim?) - in the pinnacle of bike racing no less. Beyond preposterous.


There are any number of perfectly good reasons to alter an engine's cylinder phasing and/or firing cadence, including simple rider preference. But for some reason the imaginations of fans and media were captured by a single, highly dubious one - the big-bang traction theory.


#168 manolis

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Posted 25 April 2012 - 08:36

With a few reasonable assumptions (and some data for the gas-pressure torque from Taylor's book ), below is the "combustion torque vs crankshaft angle" for the SXV (brown) and the MXV(green), and the inertia torque (blue) at the peak power revs

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Below is the resulting total torque of the MXV and SXV arrangements, at the peak power revs:

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The fat orange-brown curve is the total torque (inertia plus gas-pressure) for the SVX (screamer), the fat dark green curve is the total torque (inertia plus gas-pressure) for the MXV (bing bang).

The other curves are the inertia torque (blue), the per cylinder gas-prassure torque (thin green and cyan lines), the total gas-pressure torque (green for the MXV, brown for the SXV)

Here is the total torque (inertia+combustion) for the MXV and the SXV, and the inertia torque (blue) at top revs:

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And here is the total torque (inertia+combustion) for the MXV and the SXV, and the inertia torque (blue) at 70% of the top revs:

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V90 and I2-90 case:

Below is the combustion torque and the inertia torque of the V90 (like Ducati) and I2-90 (in line two cylinder with crankpins at 0 and 90 crank degrees, like a version of the Yamaha TDM):

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The I2-90 and the V90 with common crankpin are - as regards the torque - the same thing. It is easy to understand if you see it from the energy view poit: the torque is actually the energy that reciprocates between the crankshaft and the pistons; as the two pistons of the V90 and the two pistons of the I2-90 perform the "same" motion, the inertia torque that loads the crankshaft is the same in either case.

Below is the resulting total torque of the V90 / I2-90, in case of the BigBang and in case of the Screamer arrangement, at the peak power revs:

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The fat orange-brown curve is the total torque (inertia plus gas-pressure) for the screamer, the fat dark green curve is the total torque (inertia plus gas-pressure) for the bing bang.

The other curves are the inertia torque (blue), the per cylinder gas-prassure torque (thin green and cyan lines), the total gas-pressure torque (green for the BigBang, brown for the Screamer)

Here is the total torque (inertia+combustion) for the V90-BingBang and the V90-screamer, and the inertia torque (blue) at top revs:

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Here is the total torque (inertia+combustion) for the V90-BingBang and the V90-screamer, and the inertia torque (blue) at 70% of the top revs:

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And here is the combustion torque and the inertia torque for the V90-BingBang and the V90-Screamer, at 70% of the top revs:

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I2-360 degrees even firing and BigBang case:

Below is the combustion torque and the inertia torque of the I2-360 even firing (screamer: combustions every 360 crank degrees) vs the I2-0 bigbang (combustions every 720 crank degrees):

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I2-180 degrees case:

Below is the combustion torque and the inertia torque of the I2-180 (combustions at 0, 180, 720, 900 and so on):

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Comparison of seven two-cylinder arrangements:

Below is the resulting total torque for: the MXV (big bang), the SXV (screamer), the twin in-line even firing (crankpins at 0 and 360 degrees), the twin in-line with crankpins at 0 and 0 degrees and ignitions per 720 degrees, the twin in-line with crankpins at 0 and 180 degrees , the V90-Screamer (or I2-90-Screamer), and the V90 BingBang (or I2-90 BingBang), (all four arrangements have same pistons, for same connecting rods, same stroke, same bore etc), at the peak power revs :

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The curves of the I2-360BigBang (more correctly I2-0-BingBang) are like the curves of the single cylinder which is a good reference for the rest arrangement.

Imagine these curves as sea-waves: if the sea is calm with the green curve (MXV), the sea is calm with the orange curve (SXV), too.

Below is the resulting total torque for: the MXV, the SXV, the twin in-line even-firing (I2 with crankpins at 0 and 360 degrees) and the twin in-line with crankpins at 0 and 180 degrees, the V90-Screamer (or I2-90-Screamer), and the V90 BingBang (or I2-90 BingBang), at 70% of the revs of the peak power:

Posted Image

These curves are more close to reality as regards the "traction": when the motorcycle changes direction the rider keeps the engine at middle rev.

The small difference between the orange curve and the dark green curve causes a big difference in the "traction", the "feeling" and the laptime.
I wonder how many times worse is the "feeling" and the laptime for the other two engines (blue and red curves), wherein the difference from the big bang is several times bigger.
Are they so bad and insensitive and unsafe at corners?

Thanks
Manolis Pattakos

Edited by manolis, 29 April 2012 - 08:44.


#169 gruntguru

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Posted 25 April 2012 - 08:53

Manolis.
Thank you. I am convinced. If anything the MXV torque looks smoother than the SXV due to partial cancellation of the largest combustion torque peak.

Now - why does the MXV lack top end power? I assume its the exhaust system. Can't be that hard to design a system that combines the "magical properties" of the big-bang with the top end of the screamer. Two seperate pipes would certainly produce the top end anlthough probably at the expense of bottom end. Probably an unequal-length header system with a shorter pipe on the leading cylinder to reduce interference at high revs.

#170 PhilG

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Posted 25 April 2012 - 09:59

Its a 77 degree V twin .. where does 180 and 360 come into it...

#171 gruntguru

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Posted 25 April 2012 - 10:51

He has thrown in some curves for an in-line twin for comparison.

#172 Grumbles

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Posted 25 April 2012 - 21:33

Has anyone ever done back to back testing on a chassis dyno? With a typical "real-world" weight on the rear tyre?
Surely if one configuration has a significant traction advantage it would show up here.

#173 bigleagueslider

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Posted 26 April 2012 - 01:51

There are any number of perfectly good reasons to alter an engine's cylinder phasing and/or firing cadence, including simple rider preference. But for some reason the imaginations of fans and media were captured by a single, highly dubious one - the big-bang traction theory.


Magoo-

That's an excellent point about cylinder phasing and firing order.

Take the ubiquitous racing V8 engine. It could use a flat 180deg crank or a cruciform 90deg crank. The cruciform crank gives much smoother running than the flat crank, but unlike the flat crank the cruciform crank produces irregular firing intervals in each bank of cylinders. The flat crank gives a much better result from exhaust manifold acoustic tuning, and that's why it's preferred for V8 race engines even though its vibrations are far worse.

Engine designers made that decision, and not the drivers.

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#174 Magoo

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Posted 26 April 2012 - 10:13

As I said: The Aprilia "big bang" is not a real big-bang engine and the Aprilia "screamer" is not a real screamer in any original (?) sense of these terms. They are only "big bang" and "screamer" in a relative sort of way with respect to each other. And even that is something of a stretch as both engines use exactly the same crank phasing, merely a different firing order. Hardly surprising, then, that their torque theta analytics are so similar. Any significant difference in the performance of these two engines comes down to their state of tune.

Now please note that the Yamaha R1 is not a big-bang engine either. In fact, the philosophy behind this engine is essentially the opposite of big-bang. The R1 was merely tagged big-bang because it has unconventional crank phasing.

I think that if you take the issue of big-bang engines as popularly discussed on the Internet and elsewhere and start peeling away the layers of bad information, it's an onion. You can peel until there's nothing left.

Edited by Magoo, 26 April 2012 - 10:16.


#175 PhilG

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Posted 26 April 2012 - 11:51

As I said: The Aprilia "big bang" is not a real big-bang engine and the Aprilia "screamer" is not a real screamer in any original (?) sense of these terms. They are only "big bang" and "screamer" in a relative sort of way with respect to each other. And even that is something of a stretch as both engines use exactly the same crank phasing, merely a different firing order. Hardly surprising, then, that their torque theta analytics are so similar. Any significant difference in the performance of these two engines comes down to their state of tune.

Now please note that the Yamaha R1 is not a big-bang engine either. In fact, the philosophy behind this engine is essentially the opposite of big-bang. The R1 was merely tagged big-bang because it has unconventional crank phasing.

I think that if you take the issue of big-bang engines as popularly discussed on the Internet and elsewhere and start peeling away the layers of bad information, it's an onion. You can peel until there's nothing left.



The terms are relative to each other.. or should they be called 'not big bang' & 'even notter big bang'....

Its just a way to identify the two , in the same way and long and short stroke , soft and hard tyres etc.. one relative to the other, that is all.

I am interested to know what you would call them.

Either way i fail to see how 'state of tune' is the difference when its the same map bar for timing of the cams and ignition.

#176 manolis

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Posted 26 April 2012 - 17:19

I corrected the plots in my post 168 above.
Please take a look.

To PhilG:

In every reference about the big bang MXV, there are comments like:
"the level of grip (of the MXV) is far better than offered in screamer (SXV) mode.. but the trade off is the top speed is not as impressive as screamer , which makes better power as the revs increase."

Why the screamer makes better power as the revs increase?

Thanks
Manolis Pattakos





#177 Wolf

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Posted 26 April 2012 - 17:58

I'm guessing that closer spacing of 'power pulses' is bound to cause vibrations (if I had experience with it, I'd try to do FFT on several of those graphs to see how it affects higher frequency harmonics*), which would perhaps make big-bang engine not be able to rev quite as high as in screamer configuration.

* e.g. in flat- vs. cross-plane I4 graphs it's quite obvious that main vibration model in flat-plane engine is at engine revs, with cylinder pressures at half the frequency (torque is, because of inertia, almost sinusoidal), whereas cross-plane will have much more harmonic frequencies

#178 gruntguru

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Posted 26 April 2012 - 22:50

I would be very surprised if the top end power was directly related to the cylinder phasing. It is inconcievable that the two versions would have a vastly different FMEP. More likely an indirect effect due to interference in exhaust or intake manifolds.

#179 gruntguru

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Posted 26 April 2012 - 22:58

I corrected the plots in my post 168 above.
Please take a look.

At 70% revs the MXV now looks mare like a big-bang than the SXV.

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#180 Powersteer

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Posted 27 April 2012 - 22:46

Manolis, how about if we had a 90 degree crank on the I2?

:cool:

#181 manolis

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Posted 28 April 2012 - 07:38

Manolis, how about if we had a 90 degree crank on the I2?


Powersteer,

in the post 168 above, it has been added the case of the I2-90 degree crank (I also made one more - minor - correction in the initial plots).
The I2-90 is actually the same case (as regards the torque) with the typical V90 (Ducati like).
In the plots, in one case the camshafts are timed for BingBang (combustions at 0, 90, 720, 810 and so on), in the other case the camshafts arre timed for Screamer (0, 270, 720, 990, etc crankshaft degrees).

In the last two plots they have been added the V-90 / I2-90 curves for comparison with the rest four arrangements (I2-360 even firing, I2-180, MXV V77, SXV V77).


To everybody:

In every reference about the big bang MXV, there are comments like:
"the level of grip (of the MXV) is far better than offered in screamer (SXV) mode.. but the trade off is the top speed is not as impressive as screamer , which makes better power as the revs increase."

Why the screamer makes better power as the revs increase?

If, by proper tuning (for instance by a system like the DVVA), the Screamer "power vs rpm" curve becomes the same with the Big-Bang "power vs rpm" curve, with both arrangements having the same linear response to the throttle, what will be the "traction" difference and the laptime?

Differently: Why the better traction of the MXV V77-BigBang has not yet been combined with way wilder camshafts (bigger valve lift, longer duration, more overlap, more top end power) to become the permanent winner?

Thanks
Manolis Pattakos

#182 manolis

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Posted 29 April 2012 - 08:58

In the post 168 above they have been added a few more plots.

The twin in line even firing (crankpins at 0 and 360 degrees) is compared with the BigBang (combustions every 720 crank degrees) arrangement (same crankshaft).

The BigBang I2-360 (or more correctly I2-0) has similar torque curves with the single cylinder engine.

Thanks
Manolis Pattakos


#183 PhilG

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Posted 30 April 2012 - 21:50

I just got back from a weekend racing in germany, and we had a chat about this, over a beer or two, was as you would expect, those that have ridden them say the same as i do.
i looked at the graphs, and its all over my head, i'll stick to riding them and let you guys stick to designing them... what i will say is that putting your arse on the seat and feeling what it is doing is the best design tool there is.



#184 carlt

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Posted 30 April 2012 - 22:58

I just got back from a weekend racing in germany, and we had a chat about this, over a beer or two, was as you would expect, those that have ridden them say the same as i do.
i looked at the graphs, and its all over my head, i'll stick to riding them and let you guys stick to designing them... what i will say is that putting your arse on the seat and feeling what it is doing is the best design tool there is.


Being able to feel what ones arse is doing is usually quite important in life

I also think that the others are trying to understand What is causing their arse sensations ?

Edited by carlt, 30 April 2012 - 22:58.


#185 manolis

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Posted 02 May 2012 - 03:47

The following simple-minded question is still un-answered:

Why the substantially better traction and feeling of the MXV-BigBang have not yet been combined with way wilder camshafts?

Thanks
Manolis Pattakos

#186 gruntguru

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Posted 02 May 2012 - 05:18

Manolis
Easier still, why not simply fix the interference/breathing issues that are stopping the MXV from matching the power curve of the SXV?

#187 Magoo

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Posted 02 May 2012 - 10:36

I have no direct personal knowledge of the Aprilia but the photos seem to show separate intake tracts and a fairly straightforward exhaust system. In that case I wouldn't ascribe the difference in output to resonance or phase interference but to a difference in mapping. I'm betting the so-called "screamer" calibration is simply more aggressive about attacking MBT, giving up midrange for more peak power. So of course the other version (so-called "big bang") will be easier, more satisfying, and more productive to ride. That makes all the sense in the world.

Edited by Magoo, 02 May 2012 - 10:37.


#188 gruntguru

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Posted 02 May 2012 - 23:57

I have no direct personal knowledge of the Aprilia but the photos seem to show separate intake tracts and a fairly straightforward exhaust system. In that case I wouldn't ascribe the difference in output to resonance or phase interference but to a difference in mapping. I'm betting the so-called "screamer" calibration is simply more aggressive about attacking MBT, giving up midrange for more peak power.

If you used identical calibration you would get identical results. There must be something more to it.

On second thought, an identical map might not yield an identical calibration due to angular speed variation profile being different for the two engines. If the crank position sensor has low resolution, the interpolated position between pulses would be different for the two engines. That still doesn't stop a good tuner achieving the same peak power for the MXV.

On third thought, If the engine management system is not capable of mapping the spark individually for the two cylinders, it would be impossible to achieve the same advance map for both engines on both cylinders. The problem would lie with timing for the second cylinder to fire on tne MXV as ignition occurs during a period of rapid crankshaft acceleration (#1 power stroke).

#189 Magoo

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Posted 03 May 2012 - 01:35

If you used identical calibration you would get identical results. There must be something more to it.


I'm saying the two engines do not have identical mapping.


#190 gruntguru

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Posted 03 May 2012 - 02:06

Yeah I get that, but surely when you convert an SXV to MXV, your starting point is the map you used in the SXV. Not many racers are going to say "lets change the mapping to take some top-end power out of this thing"

Edited by gruntguru, 03 May 2012 - 02:07.


#191 PhilG

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Posted 03 May 2012 - 07:11

Yeah I get that, but surely when you convert an SXV to MXV, your starting point is the map you used in the SXV. Not many racers are going to say "lets change the mapping to take some top-end power out of this thing"



but we did.. maps were scratch written .. cams were swapped for SXV race kit parts , but the top end run out of power on the MXV was flat , nothing really at the top compared to the SVX which would keep pulling allt he way to the limiter. Map ran wasted spark, plenty of advance and loads of fuel, including fuel in on closed throttle , and point of injection was changed ... still had the same basic charateristics

#192 gruntguru

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Posted 04 May 2012 - 08:12

I think you are saying the MXV wouldn't match the SXV for top-end power regardless of what you did to the mapping.
If this is the case, I would suspect the folowing
- Exhaust - if the system is 2 into 1, the interference will be different from SXV to MXV.
- Ignition timing. The "trailing" cylinder will have retarded timing in MXV mode due to crankshaft acceleration between crank-trigger pulses being dramatically different for trailing and leading cylinders. The fewer the teeth on the crankshaft trigger, the worse this effect will be. If the engine management permits different mapping for each cylinder, the fix is easy. If not, you could change the basic setup of the EMS - try telling it the cylinders are 72 or 75 degrees apart instead of 77. This will allow a compromise with the trailing cylinder retarded in some areas and advanced in others.

#193 manolis

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Posted 04 May 2012 - 13:02

but we did.. maps were scratch written .. cams were swapped for SXV race kit parts , but the top end run out of power on the MXV was flat , nothing really at the top compared to the SVX which would keep pulling allt he way to the limiter. Map ran wasted spark, plenty of advance and loads of fuel, including fuel in on closed throttle , and point of injection was changed ... still had the same basic charateristics


The BigBang arrangement cannot – alone – justify the big difference in traction and feeling between the SXV and the MXV (graphs in post 168).

The plot below is the valve timing vs the camshaft degrees (a complete circle corresponds to 720 crank degrees); it shows the difference between the BigBang V-77 and the Screamer V-77.

Posted Image

The basic valve timing is taken as:
the exhaust valves open 70 crank degrees before BDC and close 30 crank degrees after TDC,
the intake valves open 30 crank degrees before TDC and close 70 crank degrees after BDC.

With the 1st cylinder of the BigBang at overlap, its 2nd cylinder is at the middle of its exhaust stroke (compare it to what happens in the Screamer).
The exhaust of the 2nd cylinder of the MXV spoils substantially the breathing of the 1st cylinder.

The simplest case is the single cylinder:
At high revs the inertia of the gas inside the exhaust pipe creates a vacuum that helps the fresh air / mixture to “scavenge” the “dead volume” during the valve overlap, accelerating the charge into the intake pipe even before the piston is at TDC, increasing significantly the rev limit – and the high-end power – of the engine.
For comparison imagine the same single cylinder with zero valve overlap: the air / mixture inside the intake pipe is “standstill” waiting the crankshaft to rotate for several degrees after the TDC in order the piston to create the necessary vacuum inside the cylinder; only then the fresh charge feels the vacuum and starts accelerating towards the cylinder, but this is “too late” for the high revs operation: the peak power is way less, at way lower rpm.

Now take another look at the valve-timing plot above.
Instead of having a significant vacuum after the exhaust valves of the 1st cylinder to accelerate the charge in the intake pipe (Independent Throttle Body or ITB) during the overlap, there is a significant pressure due to the exhaust of the 2nd cylinder.
Judging from the pattakon VVA-roller Honda VTEC prototype valve lift profiles:

Posted Image

at the overlap-TDC the intake and exhaust valves of the MXV are significantly open (2mm lift?), which means that the exhaust gas into the exhaust pipes (of pressure substantially higher than 1 bar) finds an alternative way and escapes towards the ITB of the 1st cylinder.
The quality of the charge of the 1st cylinder degrades, its temperature increases, its the quantity reduces. The engine is like operating with one and a half cylinders.

It seems Aprilia deliberately uses the exhaust to “chock” the MXV engine at high revs in order to improve the traction and the feeling. The MXV is for different use than the SXV.


If you isolate the exhaust of the one cylinder from the exhaust of the other, the MXV will breath like two independent singles that share the same crankshaft.
With wilder camshafts and independent exhausts, the high-end power of the MXV can be more than the SXV’s.
But this way the advantages of the MXV (better traction and feeling) will be lost.
With a specific camshaft (i.e. with a specific valve lift profile) in your engine, the only you can do is to optimise the injection and ignition maps.

For the sake of a little more high-end power, most of the tuners actually spoil the operation of the engine: after the "tuning" the engine cannot idle as before, is not clean/green as before, is not driver friendly as before, is not torquey as before etc.

Things are similar in racing: with a conventional (single mode) camshaft you have to compromise a lot.

Are you sure there is no way to combine the high-end power of the SXV with the traction and feeling of the MXV in the same motorcycle?
I am sure for the oposite.

It is now time to take another better look at the desmodromic VVA (DVVA) at http://www.pattakon....ttakonDesmo.htm .

It is like having infinite camshafts in the motorcycle, and choose each moment the perfect one.
Instead of selecting a camshaft and then trying to optimise the engine operation around the selected camshaft, you first optimise the instant "valve lift profile" (like replacing the camshaft of a conventional engine with another, which is way more vital for the overall operation of the engine) and then work on the injection and ignition maps.
You don’t need to compromise any longer, neither to play hardly with the exhaust.

With a few clicks you adjust your suspension to the race conditions.
Similarly, with a few clicks you can adjust the character of your engine (racing or not) to the existing conditions.

I read you were in Germany for a weekend racing.
The British “Engine Technology International” magazine (Dean Slavnich and his team) organizes each year the Engine-Expo-International, Stuttgart Germany (12, 13 and 14 June, this year). Pattakon may be there. If you are in Germany, come to see some interesting staff.

Thanks
Manolis Pattakos

#194 PhilG

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Posted 05 May 2012 - 00:02

I think you are saying the MXV wouldn't match the SXV for top-end power regardless of what you did to the mapping.
If this is the case, I would suspect the folowing
- Exhaust - if the system is 2 into 1, the interference will be different from SXV to MXV.
- Ignition timing. The "trailing" cylinder will have retarded timing in MXV mode due to crankshaft acceleration between crank-trigger pulses being dramatically different for trailing and leading cylinders. The fewer the teeth on the crankshaft trigger, the worse this effect will be. If the engine management permits different mapping for each cylinder, the fix is easy. If not, you could change the basic setup of the EMS - try telling it the cylinders are 72 or 75 degrees apart instead of 77. This will allow a compromise with the trailing cylinder retarded in some areas and advanced in others.


you can map each cylinder, and the sxv has a linkage that dragged the rear cylinder a little on the butterflies .. the stock system didnt allow you to do anything other than load aprilia maps, and a few tweaks, the piggyback software allowed pretty much everything .
The MXV stock system was very nice for MX , quiet and tucked away, the Arrow factory pipe was a twin pipe system , but was toast the first time you threw it up the road.. at £2500 a pop i didnt think it was the way forward, although the team owner got one, i never used it ,it is better HP wise, but thats only on paper.. i didnt get to ride it


#195 gruntguru

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Posted 05 May 2012 - 04:31

There is no reason you shouldn't achieve the same top end in big-bang mode. It may require individual exhausts or an unequal-length 2>1 system. It may also need mapping the timing for each cylinder individually. Have you tried this?

#196 Magoo

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Posted 05 May 2012 - 07:48

Getting back to the original topic, big bang engines... As I seem to remember it: In the early 90's Honda built a two-stroke V4 with a torque curve roughly the thickness of one playing card. So the firing sequence was altered to make all four cylinders fire within 70 degrees so Doohan could find the little monster's output band, thus empowering him to ride the damn thing. That was a big bang engine in the original sense of the term. The philosophy was the exact opposite of the Yamaha R1, or the perceived advantage of the Aprilia V2 as expressed here.

#197 PhilG

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Posted 05 May 2012 - 10:12

There is no reason you shouldn't achieve the same top end in big-bang mode. It may require individual exhausts or an unequal-length 2>1 system. It may also need mapping the timing for each cylinder individually. Have you tried this?


The stock exhaust is like that, the factory pipe, is equal i think, mapping for each cylinder is done, because the stock ECU runs the rear cylinder richer than the front.


#198 PhilG

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Posted 05 May 2012 - 10:22

Getting back to the original topic, big bang engines... As I seem to remember it: In the early 90's Honda built a two-stroke V4 with a torque curve roughly the thickness of one playing card. So the firing sequence was altered to make all four cylinders fire within 70 degrees so Doohan could find the little monster's output band, thus empowering him to ride the damn thing. That was a big bang engine in the original sense of the term. The philosophy was the exact opposite of the Yamaha R1, or the perceived advantage of the Aprilia V2 as expressed here.


Well that sounds exactley like the Aprilia to me.. i dont see how you get an inline 4 to be truly big bang... honda had the same with the RC30 and VFR750. The RC30 had a different firing order and a flatter power band to the road based VFR which had the more even firing order of the two. Having ridden VFR 750's , and an RC30 and an RC45 the same feeling applies , the race based bikes pull from nothing , and run out of steam top end, but i seem to recall they had a wider ratio box , and a very very tall first gear, which meant you had a bigger rev drop between gears , and kept you in the useable power.


#199 Magoo

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Posted 05 May 2012 - 11:55

Well that sounds exactley like the Aprilia to me.. i dont see how you get an inline 4 to be truly big bang... honda had the same with the RC30 and VFR750. The RC30 had a different firing order and a flatter power band to the road based VFR which had the more even firing order of the two. Having ridden VFR 750's , and an RC30 and an RC45 the same feeling applies , the race based bikes pull from nothing , and run out of steam top end, but i seem to recall they had a wider ratio box , and a very very tall first gear, which meant you had a bigger rev drop between gears , and kept you in the useable power.


You are still confusing firing sequence and torque curve. These are two different properties. Firing sequence has remarkably little effect on an engine's torque curve.

For example, on the Apilia V-twin, either firing sequence could be easily tuned to obtain the output curves that you identify with the opposite firing sequence.

The so-called Aprilia "big-bang" version could be easily tuned as a classic "light switch" engine, with a very narrow useful output band at the top of the rpm range.

Or the so-called Aprilia "screamer" version could be easily tuned as a classic "area under the curve" engine, with a wide usable output band over an extended rpm range.

This wouldn't even be difficult. It would be more difficult to tune the two engines to conform to their attributes assigned to their respective nicknames.

The truth is there isn't a great difference between the two Apilia versions in their cranktrain kinematics. Both engines employ the same crank phasing, altering only the firing sequence. This is why the torque theta analyses Manolis kindly posted here are so similar.

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#200 PhilG

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Posted 05 May 2012 - 16:10

You are still confusing firing sequence and torque curve. These are two different properties. Firing sequence has remarkably little effect on an engine's torque curve.

For example, on the Apilia V-twin, either firing sequence could be easily tuned to obtain the output curves that you identify with the opposite firing sequence.

The so-called Aprilia "big-bang" version could be easily tuned as a classic "light switch" engine, with a very narrow useful output band at the top of the rpm range.

Or the so-called Aprilia "screamer" version could be easily tuned as a classic "area under the curve" engine, with a wide usable output band over an extended rpm range.

This wouldn't even be difficult. It would be more difficult to tune the two engines to conform to their attributes assigned to their respective nicknames.

The truth is there isn't a great difference between the two Apilia versions in their cranktrain kinematics. Both engines employ the same crank phasing, altering only the firing sequence. This is why the torque theta analyses Manolis kindly posted here are so similar.



And yet the Factory Aprilia guys seem unable to do this, obviously considering its not difficult.

I've had enough, i've obviously spent too much time riding and not enough sat behind a desk trying to go fast on a graph.

I'll go and polish me clubby trophies.