30 replies to this topic

[Top Fuel F1]

I don't follow CART; but I just noticed that they are reaching these RPM's without the benefit of pnematic or hydraulic actuation or closure of the valves. That's not a lot of difference in RPM with F1, with pnematic. They are definetly using springs in that their rules talk about spring retainers and keepers. These springs must be very robust to keep the valves from floating. Also the force required to open these valves must be great, using a lot of the engine's power. Also they may have more room than F1 to house these massive valve mechanisms. Any comments from those expert on engine valves?

[Ali_G]

I heard CART were still on about 14,000. That's an extrordinary figure using Spring Valves. I wouldn't think that those sort of valves could take such punishment. They just wouln't be fast enough.

Niall

[slipstream]

Both the Ford XF and Toyota Cart Engine can rev to about 16,200 rpm , which is an amazing because their Engines are not near as expensive as those engines used in F-1.

[mhferrari]

Those springs must be very advanced to cope with 16,000+ rpms.

[Nathan]

Would Titanium work??? Are they aloud to use MMC's in the spring???

[Top Fuel F1]

CART's regulation: "Intake and exhaust valves, spring retainers and keepers are limited to titanium and ferrous alloys".

Best Regards;

[Powersteer]

My crazy theories is it that to design the Pistons exsaust valve pockets and valve coin in such a way that it actually uses the piston to push back the valves, very delicately though. As we know when an engine is over rev'ed the distruction of an engine by cylinderhead is usually down to valve floating. Through the timing nature of a four stroke engine it is indistructable for the intake valve to float slightly(totally undesireable). But when the exaust valve floats it will immediately hit the piston and KABOOM!



Another crazy theory are that the valve spring are incompressible at full lift, mean it can't make the valve overlift to hit anything. The interesting idea of this is that when the valve reaches full lift it'll bounce back through shock wave created by the spring reaching its fullest potential, like bouncing a tennis ball.


But honestly for me that is, the only way they could go too such high RPM is by using smaller valves(unless valve or spring construction has got to a new level). Remember, this would also decrease torque but the high RPM would increase horsepower. In a CART engine there is too much torque as they are turbocharged engine( for a 2 wheel drive). So why not sacrifice what is surplus for a better balance in total power.I could be wrong, just trying to have some fun here, ciao.





[p][Edited by Powersteer on 09-24-2000]

[DangerMouse]

Is there a restiction regarding valves per cylinder in CART engines? if not running eight small valves per cylinder would mean 16,000+ RPM with conventional vale gear is more than possible.

A bog standard Yamaha R6 (600CC) roadbike revs to over 15,000 stock, and the valve gear is said to be safe to over 16,000, smaller road bike four strokes have reached nearly 20,000RPM (honda 250/4)

As valve sizes are not that critical with Turbo engines I don't find these figures at all unreasonable.

[Nathan]

Im pretty sure they are limited to 4-valves per cylinder. Not 100% sure, but pretty sure.

[koenda]

for formula one:
[rl]http://www.fia.com/r...tec/F1tec-a.htm[/url]
5.1.5 - Engines may have no more than 5 valves per cylinder

but isn't the max. rpm dependant of the stiffness of the valve spring? I believe that the valve floating depends on the frequency of the natural oscillation of the mass-spring system?

[Top Fuel F1]

The CART V8 is mildly turbocharged to a maximum of 40 in. Hg absolute (4.95 psi guage). CART's regulation: Maximum of 4 valves per cylinder.

[DangerMouse]

koenda, with conventional valve gear the maximum revs are dictated by recipricating mass, the lighter the valve the higher you can rev, as Turbo cars are not that relient on valve area compard to NA engines I still think 16,000RPM is not unreasonable as the CART engines could run reletively small valves (with not too extream lift) and still produce decent power as they are Turbo charged.

[koenda]

the natural frequency of a mass-spring system depends on the stiffness of the spring, and the mass. You can reduce the mass to give it a higher natural frequency or increase the stiffness of the spring.
I think if you want to run at higher rpms with a turbo engine, you also need the max. area. Otherwise the cylinder can not get a decent volumetric efficiency (in normal words: the cylinder cannot be filled enough). The air speed would be too high and choking might occur. The cylinder can not get enough air and this would limit your rpms.
Your turbo also has to produce a higher pressure because of the restriction by the valve, this reduces overall efficiency because the exhaust gasses have to have more energy to drive the turbo.

[DangerMouse]

The stiffness of the spring can be reduced directly proportionally to the weight of the valves and their retaining clips etc. This results in a higher rev ceiling (as long as valve bounce can be controlled) with less mechanical loss toboot.

The whole point of Turbo charging is increasing VE without any other modifications - if that wasn't the case Turbos wouldn't do anything.

I'm not saying it's the optimum (for peak power) to have less valve area with a Turbo - but it hurts less than with a NA engine which soley relies on the natural gas flow through the inlet valves to determine how quickly the cylinder can be charged (helped a little of course by the kinetic energy of the gases leaving the exhaust port sucking in fresh mixture) - this is what currently limits F1 engines, not valve-gear rev ceilings. VE is dropping off at ultra high revs as there is not enough time to fill the 300CC cylinders regardless of valve size with a NA engine.

The move last year to circumvent this problem by again developing 12 cylinder engines was banned by the FIA.

Brian Hart had 20,000RPM F1 engines on the bench years ago - he came to the conclusion then that 12 cylinders was the only way to go in F1 as power dropped of past 16,000ish RPM (due to poor VE) and campaigned to develop a 12 cylinder for Arrows which never happened.

Of course the nature a NA engine sucking in its air means the density of the air is reduced and corrospondingly the VE is never very good except at certain rev ranges where the engine will be pulse tuned. Turbos always have good VE whilst on boost across their rev range.

I should image being that there is a boost limit in CART engines that they look for revs as a way of maximising power in the same way you would with a NA engine, and playing with valve area against max revs is probably the best way to it.
The whole reason quite a few Low Pressure turbo engines have popped up in resent years (Volvo, Saab, Citroen, Rover) is you can have low valve area maximising burn and so torque at low revs with the Turbo giving back the power dropped by the low lift cams and small valve area higher up the rev range.
Drivability with power - sounds like a CART engine.

[Marco94]

DangerMouse,

Turbo charging uses the energy left in the exhaust gases to get extra mixture into the cilinder. It improves the mass flow in to the cilinder. They were no invented to improve volumetric efficiency. Volumetric efficiency is related to the losses that occur during the transportation of the mixture from outside into the cilinder. So the volumetric efficiency is measure for how well this increased mass flow is transported into the cilinder.

As far as the valve mass and springs are concerned, reducing the mass and correspondingly reducing the stiffness bring you nothing. Valve bounce is caused by the mass-spring system of the valves will resonate. It will move in its eigen frequency. So the trick is to make this eigen frequency higher, so that you can rev higher as well. The idea you mention, keeps the eigen frequency equall and therefor you can not rev higher.

The down side of this is a greater machanical loss in operating the valves. Due to the higher stiffness, the forces for operating the valves are higher as well and consequently the losses.

Marco.

[koenda]

Thanx Marco,

I suppose I should have written more words to make it clearer. But that's what I meant to say.

It's true that the rpms are limited by the maximum flow through the intake system, but that can be improved by redesign. Bigger intake-manifold, larger valves, firing order, valve timing and so on. You can get more air in by reducing the discharge coefficient (or friction in the intake-system) or tuning the intake-system. Then it uses the compressionwaves caused by opening and closing the valves.
But the effect of the limitation by the maximum flow is not as important as the floating valves. Because this does not harm the engine, the power is reduced because of the reduction of burned mass. So you have to shift earlier.
Hart should take another look at his conclusion, because the McLaren runs at 18+ krpm.

btw Marco: EIGEN frequency

[Marco94]

Koenda,

Ehhhh.....

[koenda]

I believe the correct translation is Natural Frequency.

for some explanation:
http://www.sci.qut.e...Zoran/mass.html
officially it should be a mass-spring-damper system, but the damping in the springs is negligible. Also, the system described in that page is force-excitated while the valve is displacement-excitated. (with a force-excitation for return ;))

[bugeye]

I know this is a bit of a rat hole, but.....

Not sure I understand this (quote below)...can somebody explain how small valves help torque ? Lift and Duration I understand, but what difference do the smaller valves make? or am I reading "low valve area" incorrectly and actually we are talking about the lift,duration,size and number of valves as a package?

Dangermouse Says:
The whole reason quite a few Low Pressure turbo engines have popped up in resent years (Volvo, Saab, Citroen, Rover) is you can have low valve area maximising burn and so torque at low revs with the Turbo giving back the power dropped by the low lift cams and small valve area higher up the rev range.


Thanks

Dave

[Powersteer]

You never know but maybe they just bolted massive valve springs to add strengh, because i don't think they use all the area possible, ciao

[koenda]

The large flowarea of bigger valves only helps in the high-rpm area because in the low-rpm area is more time available to get the air in the cylinder. (the valves are open for a longer period)
Because of the smaller valves you can use less stiff valve-springs. And this reduces the friction of your camshaft. resulting in reduced powerneed of the camshaft, so you get more torque.

In the high rpm area you can't get enough air in with small valves, so a boost-pressure might help here.

[Billy Gunn]

Once more into the Rat Hole!

Bugeye - Small valves help low speed torque due to the resulting optimum discharge gas speed being reached at lower rpm. 90-110 Meters per second gas speed is often quoted as the optimum.

Dangermouse - If Brian Hart was so keen on V12's why did he perservere so long with the V8? When did he run a 20,000rpm engine (must have been a glo-plug model airplane!)from memory his V8 only gained air springs in '96 when Arrows funded the work. I thought the argument within Arrows for a V12 came from the Tech Director (M Coughland), as the narrow track cars of '98 onwards required a longer wheelbase he argued for a longer engine (V12) which was narrower (60deg Vs. 72deg). This was from an interview back in Autosport magazine mid last year.

Valve spring technology is very advanced in the US, it's not uncommon for triple springs to be used with the third and intermediate spring being a flat spring wound between the inner and outer and acting as a surge damper. Rousch NASCAR engines use something like 900Lb seat load, with 1,700Lb at full lift - full lift being around 1". These engines run massive valve sizes, typically 2 1/2"+ inlets, and rev to 9,000. Look closely at a NASCAR engine and you will see more oil piped to the valve gear than to the crank, as these sort of loadings mean valve gear lube is critical (as well as getting the heat away). Although these high loadings mean high parasitic losses during valve opening, the recovered energy is still in proportion.

Besides didn't Honda run a 3 cylinder 50cc race bike engine back in the '60's at near 30,000 rpm on spring valve gear?

To sum up - if you design the spring correctly the natural frequencies can be diminished, and while we're here let's get our terminology straight - there is a world of difference between valve 'float' and valve 'bounce'.

Hangyerganzieontneckiesneck

[bugeye]

Thanks BG,

That explains in perfectly...


Dave

[DangerMouse]

BG, Hart persevered with the V8 so long as the block and crank was basically that of the Cosworth DFV, he simply fitted Hart heads to the engine - it’s called a small budget operation reusing old technology.

The Autosport article you refer to is ions put of date, Hart was bench testing 19-20,000 RPM V10s back in 1997 – they were not reliable (or developed enough) to be run in a car – the fruits of this project became the Arrows V10 – a hopelessly under-funded project that was always intended as a stop-gap, Tom Walkinshaw screwed Brian Hart.

Small valve area increases torque by nature of ensuring high speed air flow through the small ports which improves fuel atomisation. And lessons fuel dropout, these two bugbears are the main culprit for bad fuelling at low revs with race tuned engines. (the other being large valve timing overlap)

Back to the Turbo thing as Turbos compress air (which is their very purpose) you can pass the same amount of air as a NA engine though a massively reduced inlet valve area. The CR of a normal engine would have to be in the region of 18:1 to match a turbo charged unit regarding packing so much air into such a small area – also valve area would have to be massive to allow the flow compromising both low speed running and the ability to rev – double whammy. Plus as the heat generated with this massive amount of compression would rule normal petrol out of the equation. (unless direct injection was used) even then the combustion would be so violent engine failure would be a certainly - petrol is too volatile for this kind of environment.

Plus the mechanical losses of compression ignition engines greatly reduce their effective power output (as does their inability to rev due to tremendous crank flex induced by the physical effort of compressing so highly) the waste heat used by the turbo is almost free energy and the mechanical CR of the engine can be very low, lowering mechanical losses.

Marco94 yes we know building high revving valve gear is all about controlling natural harmonic frequencies (or at least keeping them out of the rev ranges we want to use) nether the less as I said lighter is better and directly proports to increased rev ceilings as long as we do not have interference frequencies caussing us headaches.

[Halfwitt]

Originally posted by DangerMouse
the Arrows V10 – a hopelessly under-funded project that was always intended as a stop-gap, Tom Walkinshaw screwed Brian Hart.

This is the reason that Brian Hart finished with racing and sold his business. Walkinshaw owed Hart massive amounts of money, even very early on in the season. Hart was threatening court action fairly early on during their 'relationship' just to get paid what he was owed. Walkinshaw just walks all over people. I used to think his successes were great, but now I hope he falls flat on his face. There are a lot of people would like to see Walkinshaw in trouble, and I bet Brian Hart is one of them.

[Marco94]

Dangermouse,

I was trying to explain to you that reducing the stiffness of the spring because you have reduced the translating mass of the valve will not change the eigen frequency and therefor not result in a higher rev ceiling.

Also it was my impression that the Hart V8 had a 75 degree block angle, and therefor could not have been a DF? development.

Marco.

[DangerMouse]

Marco,
Reducing the Valve weight (and therefore spring rate needed to keep it against the cam profile) will result in a higher rev ceiling simply due to the resulting mechanical stress on the valve means it can take more punishment before failing, the reduced reciprocating mass means less valve bounce sue to a simple fact of less kinetic energy.

The Hart thing is quite complicated! He originally developed the DFR using his own heads (yes I know it had a 90 degree V angle! ) and then developed his own engines based of the cylinder head of the DFR designs (I think for CART and F1?) - as far as F1 engines are concerned he actually produced the V10 first (93) and then lopped two cylinders off in 95 to bring it back down to 8 cylinders as a packaging exercise, he then returned to the V10 format again in 98 with a new block design to save weight.

It's a shame Hart got absorbed into and asset stripped by TWR, TWR forced him into being taken over in the first place simply by not paying him for months until he got in serious financial striff and then offering the 'partnership' that saw his F! design shop absorbed into the TWR engine facilities the V10 run for a whole season with little development, which was then put in moth balls.

Hart is now left unable to pursue his love (F1 engines) unless TWR can persuade AMT to joint forces with TWR for development.

A real shame. Hart, I'm sure, would with the right backing be able to perform the same miracles Illmor managed with Mercedes money.

Toyota would be wise to buy Hart out of TWR.[p][Edited by DangerMouse on 09-28-2000]

[Marco94]

DangerMouse,

Lets just agree not to agree. I am not satisfied with your explaination of things, but have not been able to convince you of my explaination either.

As far as TW is concerned. He has pulled the same stunt when he could not buy Ligier. He had planted lots of TWR guys there. When he realised Guy Ligier would not sell, he called them all back. Leaving about half the original amount of engineers.

Marco.

[DangerMouse]

Fair enough! at least we agree on TW - what a weazel!

[Marco94]

When I say he called them all back, that was literally. The call came during the day and the next day only half the Ligier team was left over.

Marco.

[Powersteer]

Why would anyone want to build a 75 ° V8??????