Quote:
Originally Posted by richard in NC
Lastly, I'd bet the turbo cars have a lower torque peak, and likely RPM peak than the NA cars.
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Richard, I generally agree with your statement based on building NA engines during my wasted youthful developmental years. And thanks Dr. Stig for the physics class (and yes, torque is King!).
Typically there's a trade off between engines designed for a high RPM power curve and the lower RPM torque. There are many factors in the engine design but they come down to: 1) bore and stroke - longer piston stroke tends to favor torque and a short piston stroke favors higher RPM horsepower generation, and, 2) the second factor is intake air/fuel volumetric efficiency.
The first is how fast the piston travels in the bore. A longer piston stoke is slower but generates more torque throughout the entire combustion cycle, i.e., n54 engine. Typically "torquey" engines have lower red line RPM limitations. The shorter piston stroke can turn the crankshaft faster and thus makes more HP at higher RPM but sacrifices low end torque, i.e., M3 s65 engine. Typically speaking, M3 Formula 1 style engines have a much higher RPM limitation.
Intake volumetric efficiency is the amount of air/fuel you can stuff into the combustion chamber at a given RPM. It is also tuned for a specific RPM range. This is still true now days, even though they play tricks with the intake manifold tracks. Put it simply, you like to feel a nice engine response when you step on the gas. But are you stepping on the gas off idle at a stop light, or in 2nd gear pulling out of a curve with the engine racing at 7000 RPM. The intake track has to be designed differently depending on where you want the power band.
To sum it up, yes I understand the power equations. And yes, I'm simplifying the discussion by saying that torque is the number to look at, but I realize the design tradeoffs the BMW engineers made in designing the N54. Looking at the n54 and its performance characteristics, its design purpose is to produce huge amounts of easily accessible torque in the lower RPM band, which is exactly where daily drivers live.