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Originally Posted by swamp2
Bruce what the heck am I missing when you agreed with some (and disagreed with other) points on my list which provided advantages (in general) of high rpm engines? My review of our discussion reveals we were talking both about the specific comparison of the Vette vs. M3 engine as well as the generalities of a "high rpm design" vs. "lower rpm design". I certainly do not agree (concede) with you that there is no advantage whatsoever for the M3 design in comparing the Vette and M3 engines. Of course you must compare engines and redlines and tranmissions as matched sets which surely complicates matters. Drop the Vette engine in the M3 without changing the transmission and you have a car with a top speed less than 130 mph.
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My review says that I was discussing a direct comparison, one engine to the other. That's neither here nor there, however. Just another of those annoying misunderstandings. I get about 147 MPH, by the way.
Quote:
Originally Posted by swamp2
How about this basic observation of the performance obtained by the systems, rather than the engines purely in isolation:
Performance tests show very closely matched acceleration figures for the cars. The M3 accomplishes this with more weight, less power, less torque and a substantially worse power to weight ratio. Could there be some advantage of the high rpm design linked to an appropriately matched transmission that contributes to making the car a much closer competitor that one might guess.
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Nope. As I've mentioned several times in this forum and this string, the M3 is pretty much an overachiever. It's not directly as a result of the high rpm design, however. A cursory look at the engine speeds before and after each shift shows that the Vette still enjoys an advantage - except at higher speeds where the closer gear spacing of the bimmer (typical of Euro designs) makes it run comparatively hard against the Vette's EPA-friendly design.
I think the M3 does a little better than expected against the Vette because it has less rotating inertia at lower speeds (see Gillespie), and closer gear spacing at higher speeds.
Someone else recently wrote a semi rant against the 6-speed in the M3 (in a DCT comparison string, I think), but to me the gear spacing is classic - and classically good. The Vette box, though very heavy and with very high rotating inertia (see Gillespie), is pretty good for American roads, but it would be a lot better if they hurled the gearset from the Mustang GT500 (the supercharged one) into it. Much more intelligent gear spacing.
Quote:
Originally Posted by swamp2
Is there some reason that F1 cars do not use relatively low rpm designs? If such designs were better in all regards as it seems to be your contention then surely such "technology" would be used in such cars. Sure neither a Vette nor M3 is as purpose built as an F1 car but all purport to offer one of the same clear and ultimate goals - very fast around a track.
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When you are restricted to particulars in a race class, high rpm equals high horsepower. My comparison was and is between specific engines.
Quote:
Originally Posted by swamp2
P.S. My take on the hp per liter thing is clear (or I'll make it clear now). High hp/l is a technical achievement and engineering advantage that may or may not always translate to a concrete/real world advantage in comparison with a lower hp/l design implemented in a properly designed and matched system.
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Completely agreed.
Bruce
PS - One area where I completely take my hat off to BMW with this engine is the exceptionally wide torque curve. It only drops about 11% (33 pound feet) from peak over a 4400 rpm span. Amazing! This is an engineering achievement, and perhaps a milestone. They apparently sacrificed a bit of maximum torque production (74 pound feet per liter as opposed to 82 pound feet in the E46) for this amazingly wide curve. I say
This engine gets the most performance from the torque produced.