[CJD Automotive]

Think of flywheel weight as an inertia weight. The heavier mass of a flywheel helps to keep the rotating assembly turning when loaded, Moment Of Inertia. Old tractors used massive flywheels that allowed low output engines to perform without stalling. So the engine is slow to lose rpm, but also slow to accelerate rpm. That's the balance. Heavier cars need more flywheel mass to keep from dragging down the engine rpm and stalling when accelerating from a dead stop. Lighter cars need less. Race cars want as little as possible so they can accelerate the engine quickly, i.e off turns and between shifts. Ever watch race cars leave the pit? They don't leave at 5K+ rpm and spin tires because it looks cool, if they don't rev the engine high when leaving from a dead stop, it will stall, because of the low flywheel/clutch weight (MOI).

I'm sure others can explain it better!

Ideal weight is subjective. Some people find cars difficult to drive that others don't. From my personal experience, 30lbs total clutch/flywheel weight is about as low as comfortable for a street car in the 3500 lb. range. Mid to high 30# seems to work best for most people on street cars. Again this is subjective, I promise someone will jump on and say they use a 7-1/4" clutch with 20# total weight clutch/flywheel and it drives like a new car...

Most new cars, Mustang, Corvette, Challenger, etc, use clutch/flywheel combo's in excess of 50# total flywheel/clutch weight.