Got a question that has bugged me for years and I figure you guys can answer it. Been an F1 racing fan for years and recently came across some engine specs and this comment. As you know, the F1's are turning up to 20K rpm's. I've read that the actual stroke is a mere 2 inches, or something so short like that and the comment I heard was "the short stroke allows for that type of rpm". Now, as the cam shaft spins around to open and close the valves, how can the valves actually keep up with that kind of crazy rpm? Wouldn't they start to float at such high rpm's? I mean, I can almost see if the engine had a longer stroke and allow the valves to get fully seated for a good strong compression stroke, but at that rpm, there just isn't any time. I mean, alcohol burns faster and all, but at that rpm, we're talking nano-seconds. I know these engines are not efficient, but some of these stuff seems like it defies the laws of physics.
15K rpm and short strokes, how so fast?
- Thread starter Schmoe
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Yep, that's some hi-tech stuff. I watch F1 regularly and they talk about that stuff. Supposedly, the lifters/valve assemblies are pneumatic. Other components may be as well. By the way, pneumatic failure is a common cause for an early end to one's race.
A) the stroke of the old V10 engines was closer to 38mm with a cylinder bore in the neighborhood of 100mm. This is a very short stroke, primarily limited by the need for a good shape in the combustion chamber and high compression with very short strokes.
B) the valves are closed with 3000 PSI of nitrogen in a cylinder topped by the valve retaining bucket (e.g. not springs)
C) the valve lift is about 60% of the piston stroke
D) the V10 engines were primarily RPM limited by the stresses in the block due to the vibration inherent in the V10 engine architecture. Several of these marvels used balance shafts to quell the vibration patterns.
With this kind of valve structure, the valves are prevented from floating by the pressure in the nitrogen tank. In the V10 engines, the valve RPM limit was above 20,000 RPMs.
Renault is to be credited with the invention of pneumatic valve actuation in F1 engines (early in the 1.5 litre turbo era). This earsed the 14,000 RPM limit of the older 3.0 litre engines with steel (or titanium) valve springs, and enabled the naturally asperated F1 motors to cross the 200 HP/limit arena into the almost 300 HP/litre arena we saw last year. I suspect that the new V8s will shortly be at the 320 HP/litre and will achieve 335-340 HP/litre before long.
Production sport bikes just crossed the 17,000 RPM barrier, and are basically limited by the metalurgy in the valve springs. Here we have streetable motors with over 200 HP/litre and ones that the manufactures will give out good warentees upon.
B) the valves are closed with 3000 PSI of nitrogen in a cylinder topped by the valve retaining bucket (e.g. not springs)
C) the valve lift is about 60% of the piston stroke
D) the V10 engines were primarily RPM limited by the stresses in the block due to the vibration inherent in the V10 engine architecture. Several of these marvels used balance shafts to quell the vibration patterns.
With this kind of valve structure, the valves are prevented from floating by the pressure in the nitrogen tank. In the V10 engines, the valve RPM limit was above 20,000 RPMs.
Renault is to be credited with the invention of pneumatic valve actuation in F1 engines (early in the 1.5 litre turbo era). This earsed the 14,000 RPM limit of the older 3.0 litre engines with steel (or titanium) valve springs, and enabled the naturally asperated F1 motors to cross the 200 HP/limit arena into the almost 300 HP/litre arena we saw last year. I suspect that the new V8s will shortly be at the 320 HP/litre and will achieve 335-340 HP/litre before long.
Production sport bikes just crossed the 17,000 RPM barrier, and are basically limited by the metalurgy in the valve springs. Here we have streetable motors with over 200 HP/litre and ones that the manufactures will give out good warentees upon.
Mitch, if you're refering to the 06R6 with the claimed 17.5k rpm rev limit, sad to say it revs slightly over 16k (as read from actual sensor pickup) before the limiter kicks in. The dials are optimistic. But 16+k rpm is still insane, and the extra rpms should be unlocked with a race ecu.
The cams turn 1/2 speed and the intake and exhaust take turns so the actaul open and close event isn't 18k or 28k or whatever. Springs have be good but the weight (mass) of the valve train has to be low to be able to control it. The ramps on the cams have to be slow so they can keep contact. Pneumatics solve a couple things like spring life and also allow more agressive ramps on the cam profiles (more power). At full boogie the valves may not be staying on the ramps completely but are more like "vibrating" at the right frequency.
I wonder if any are using a desmodromic valve train.
[The valve has a very light spring, and opens and closes with dedicated cam action]
[The valve has a very light spring, and opens and closes with dedicated cam action]
Race cars use all sorts or weird technology. I know some drag classes that limit you to stock lift actually end up using valvetrains specifically designed to throw the lifter up off the lobe and catch it on the way back down in order to get the valve open further while still adhering to the lobe lift and rocker ratio rules. Point is in racing sometimes they embrace the "out of control" rather than try to control it.
mechtech I think Ducati is the only one with desmo valvetrains these days, though I could be mistaken
Ducati is the only engines that currently use a desmo system, an old Mercedes (?300 SL?) used them also. Desmodromic valves were a useful advancement when valve spring metelurgy was still in the 1950s, and not so now.
It's ironic that Ducati is the only bike mfg using the desmoronic system with its extreme high rpm ability, but their engines don't rev. After doing a couple valve adjustments on them - I much prefer the traditional shim under bucket design - and it has been proven that with light weight valves and good springs high RPM's are very achievable with the traditional setup. I have a bike at home (a dinosaur some would say) that revs to 13,000 rpm with rocker arms and threaded lash adjusters.
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