A lighter flywheel means less rotating mass. Which can give you more power. You will mainly see this power on the high end. But from what i've been told, it accelerates engine wear. They are kind of like harmonic balancers... I would just leave it alone..
<font size=-1>[ This Message was edited by: 66stang on 2/7/02 3:50am ]</font>
I could swear I read something to the affect that the lighter fly wheel because of its lesser mass allows the motor to rev faster but you loose inertia that translates to the rear end, kinda like loosing torque that would other wise be tranlated to the rear end.
Dont read anything into that, I am just repeating what I think I remember about the article.
if it's a street or drag car, leave it stock, or even heavier than a stock one would be nice. The lighter ones are good for road racing where the engine is constantly accelerating/decelerating (the ligher mass makes it "easier" for the engine to do so). Actually, in drag racing, a heavier flywheel is better. When you dump the clutch at for instance 5000 rpm, the engine wont drop as many rpm due to inertia as it would if the flywheel was 20 pounds lighter. This will make the car leave the line better, traction permitting.