I would like to ask also, what is the point of a lighter flywheel? In motorcycles, it's common to add a heavier flywheel, to smooth the powerband and make the engine more tractable.
Why is this not desirable with cars? The lower weight of the flywheel doesn't add power.
Motorcycles
tend to have a) way high power output relative to weight and b) in all but ideal surfaces a "problem" of finding grip for both acceleration and braking.
Only place I've seen flywheel weight added is on loose surfaces, like mud, or rockier surfaces.
And there it is wonderful...or more accurately the lack of enough "schwungmass" is a real pain.
Cars
TEND not to have excess power and they
tend to have lots of grip.
Again except on loose surfaces--where the real fun is---like gravel roads..Now there some "reasonable" flywheel weight is desirable, especially iif the motor has some 'reasonable" powerz...
But EVERYTHINg that rotates counts..from front pulley, crank, flywheel, pressure plate, disc, gears and shafts n the box, prop shaft, diff, halfshafts wheel tire package...
And then there's the question of "what's Light?" and "what's 'heavy'?"
At 30.7 or 31.4 lbs the dog dish thing is, for a 2,3 engine in a car fawkin heavy
Flywheels in the 8-9 lb range are ridiculously light...
14lbs like the steel ones I made are light but not silly...
Another thing which comes into the equation is what are the gearbox ratios?
Got super wide ratios, you want more swung mass...
Got real close like 2.25:1 first and 1:1 top, you want somewhat lighter...
I still say its all a little wanky since the flywheel always is rotating in the same direction...so it picks up some percentage of rpm but its not like the thing starts and stops 4 times every complete 720* cycle....some things do..And slowing a piston and half of rod weight at TDC then starting it down, then stopping it at BDC again and then starting it again now that costs power..How much? Guys with more math skills can tell you that but just thinking...and looking at every modern motor after say 1988 says there's somehting there cause evrybody has made great efforts reducing reciprocating weight.
But in the end my main gripe is I ain't a fan of cast iron flywheels, light or heavy..
Steel.. nuff said.