AntoRS4 wrote:
first at all, you lose some hp somewhere...
700hp / 2400cm3 / 18000rpm x 4163cm3 x 7800rpm = 526hp ( great result... 27% more that a stock 415hp rs4 )
30% is exactly the extra pressure that you can have into the intake manifold if the engine is perfectly tuned to take advantage from the intake/exhaust pressure waves ( this is not reported on your bosch handbook )
to tune the lenght of intake and exhaust pipes, the volume of the plenum and the lenght of the ram pipe is not easy, you also need to take in consider the cam timing and overlap period,and last but not the least the intake and exhaust air temperature ( this change the sound speed and so the resonance frequencies) . If all the parameters are correct you will have some extra positive pressure points in the rpm scale.
Intake air temperature and exhaust pipes temperature are the first parameters that can change ouput values on a dyno.
Dyno software corrects the power output for the effect that temperature has on the air density sqrt( (273+ Tin)/( 273+15°) ) , but can not correct the effect of the resonances that can completely disappear if the temperatures drive the acoustic tuning inside the pipes.
I know that seems strange but you have to know that the positive pressure waves ( that run at the speed of the sound ) must fall exactly in the cam overlap time ( that is very short ) so just a little change into the sound speed will compromise the entire system.
This is the reason because you can repeat dyno runs with same output results on engines that don't take advantages from the acoustic induction system.
If you are able to mantain the intake manifold and exhaust pipes temperatures you will obtain the correct values also on a rolling road dyno ( not easy )
From my experience a stock RS4 engine, with clean valves, with polished and shaped intake ports can reach a 5/8% extra pressure and apx 420hp.
If valves are not clean the cam overlap time will be decreased near to 0 with the effects that you already know...your engine will lose the 8% intake extra pressure (so 8% in output power).
If you are so unlucky the exhaust back pressure wave that can not cross at all the cam overlap to reflect itself into the intake runners/plenum, will stop into the cylinder filling it with exhaust gas instead of clean air (with more power lost).
Race engines have very wide cam overlap periods because they don't have to take care about pollution effects.
A wide cam overlap period with correct pipes sizing can produce 30% and more extra dynamic pressure.
Hope my poor english can help somebody to understand how a racing engine differs from a street one.
Some terms, formulas and concepts are banally explicated in the intent to give an easy explanation of the complex phenomena that the induction system is.
For all of you that are really interested in it and not in chiptuning bullshit, and if you have good physics and math knowledge, you can take a look at the SAE web site, lot of good books for dummies and not.
no HP/numbers lost, your logic/math is wrong...
you can't calculate the F1 vs RS4 HP that way using ratios...for 2 reasons:
1 you must calculate the torque first, then the HP...if you do, you'll see the equations hold true...also you have'nt factored in the F1 cars Cr anywhere...
2 you're assuming the engines are designed the same...they are not,
2 different design requirements, road car vs race car, ie, torque curves, wide power band, vs narrow range...
iirc Cr for an car F1 Mep approaches 16:1 (with the ram air effect)
T = 146 in^3 x 220 lb/in^2/4Pi ~ 2,822 in-lb ~ 235 lb-ft
iirc an F1 engine makes ~90% T at HP peak
HP = 0.90 x 235 x 18000/60 x 2Pi ~ 398,668 ft-lb/sec
HP = 725
with 5% losses ~ 690...very close to 700, considering the assumptions, surprisingly so...
you are saying the valve buildup decreases volumetric efficiency...
it may, but it won't affect it by >10%, besides, the mep is only 1/2 of the torque equation...the volume of the engine does not change...
with the valves fouled I bet you see no more than 1% decrease in Vol eff or pumping losses...
again, these equations are absolute...
another way to look at the torque is the piston area and mep...
in^2 x lb/in^2 ~ lb thrust...taking this as a moment against the crank throw (lb x in = in-lb, convert to lb-ft) will give a reasonable approximation of torque...
RS4 Bore = 84.5 mm area ~8.7 in^2
S = 92.8 mm or 3.65 in, moment calculated from arc length of throw ~ 2.3 in
T = 12.5 x 14.7 lb/in^2 x 8.7 in^2 x 2.3 ~ 3,677 in-lb or 306 lb-ft
again, very close....
