Originally Posted By: HTSS_TR
HP/L tells you how advance the engine is at the time it was designed. HP/L complied with tough US emission control is even harder to do.
...
If you think Honda S2000 engine is over-hyped, 240 HP 4-cyl is useless such that Z4 2.5L can beat it on any race circuit, do you accept my challenge ?
HP/L doesn't, IMO tell you much at all.
Let's recall... HP is effectively a derived number, not really based in any fundamental physics.
A horsepower is a unit of power equal to 746 watts or 33,000 lb-ft per minute (550 lb-ft per second).
HP = rpm x Torque/5252
5252=33,000 divided by 3.14 x 2 = 5252 (DISTANCE per revolution = RADIUS x 2 x 3.14, and we know the radius is normalized as foot-lb).
So its all about torque...
To get 300 HP at 9000 RPM would require around 175 lb-ft of torque. To get the same power at 5000 RPM would require approximately 315 lb-ft of torque.
I don't know, plenty of older cars were able to get over 130 lb-ft of torque from 2.0L. 175 doesn't seem like much of a stretch from there.
What is impressive is working at 9000 RPM. Ill grant that. The reciprocating parts need strength to overcome the pounding and the elongation forces, while the rotating masses need to have enough strength that tip speeds at those RPMs don't rip them apart. That's relatively easy in exotic engines with routine repair and replacement intervals and expensive, special materials. In a low cost consumer car? Not as much. So doing 9000 RPM and still being smooth and capable as a daily driver is a nice trait.
But that said, low torque at high rpm to make a HP number isn't that impressive to me. Its uncomfortable, inefficient, and has other potential lifecycle issues. But like anything in engineering, everything is a tradeoff...
So to say x hp/L from a super fast spinning engine is great, well, maybe its impressive in some ways, but its not all that wonderful in others...
Its really no different than saying that oil a is better than oil b because oil a has 60% PAO while oil b is 60% group III, when in reality, oil b performs identically, has the same or better oxidation resistance, and can carry more additives. Yes, on some grounds oil a is better. But in the big picture, all these numbers are just that, numbers. An S2000 is an interesting and good car, but not necessarily because of its HP/L numbers. A BMW is also an interesting and good car, but just because it doesn't spin at 9000 PRM and make the same hp/L doesn't mean it is less worthy. Each will have its fans, and each will have its critics...
