Highway MPG

[fumesucker]

Originally Posted by theholycow

Imagine a 5 liter V8, and a 2.5L I4 made exactly the same - same bore, stroke, even the same head, just appropriately different cam and crank to keep the firing order even (unlike 1970s Buick V6 oddfire). At any given RPM, the V8 would have to make approximately double the power; and at any given amount of power, the V8 should run at half the RPM. So, given twice as tall gearing, the V8 should use approximately the same amount of fuel to cruise at the same speed.

Engine friction rises non linearly with engine rpm.. I suspect it's close to a square ratio like aero drag. This means the four cylinder turning twice as fast will have more than twice the friction.

When BMW set out to design a fuel efficient version of an existing model in the very early 80's, they used a six cylinder and actually increased the displacement from 2.5 to 2.7 l. Low spring pressures in the valve train, fewer bearings, low rpm torque and high final drive ratios.

In addition to engine efficiency, the Corvette's drag coefficient is .286 vs. the WRX's is .33 to .35 (depending on trim level).

For P&G a Corvette can be thought of as a kinetic hybrid with a large storage system and a very powerful engine.