Originally Posted By: taurus_sable
people often mention the more powerful v8 has a lower rev than a less powerful v6 at the same speed.
I don't understand this because I thought the rev is determined by the wheel size and transmission gear ratio, if both are the same for v6 and v8, should an v8 still have lower rev at 70miles than a v6?
You are correct: engine revolutions per minute at a certain vehicle speed are determined by tire circumference and mechanical advantage (gear ratios). The engine size or type has nothing to do with it.
That said, I think what folks MEAN if they say something like that is a vehicle with a V-8 will usually spin slower at a given speed because the vehicle manufacter can set the gear ratios so that happens. V-8s often produce more torque at lower engine speeds than engines with fewer cylinders, so to optimize fuel economy, the gear ratios can be set such that the V-8 does turn relatively slowly at a given road speed.
This isn't always the case. Our Acura's V-6, for example, spins at only 2,000 rpm at 75 mph. Our former V-8 powered Cadillac STS would be at about 2,500 rpm at the same road speed. In general, it's probably true that most vehicles with V-8s are geared "taller", but it's certainly not always true.
