Is it true that if you have a lighter flywheel say 10lbs, one of the major disadvantages is the loss of torque?

 

No. It will actually help, especially in 1st and 2nd gear.
I don't know why this myth is so spread out. A heavier flywheel requires more energy to spin, because of the greater inertia it has. A lighter flywheel has less inertia, and thus requires a least effort from the engine to get it spinning.

What it will lose though, is a good idle.

 

loss of inertia

 

yes it is somewhat true.

 

Not true at all. Your engine already puts out a certain amount of power through the tranny. Lightening the flywheel actually transfers more of that power to the ground. Idle does kinda suck a little but no big deal; you get faster revving throughout the rpm's. RPM's also drop between shifts if you don't give it a little gas. Also starting the car from a stop, you will need to rev a little higher to not stall or bog.

 

what do you guys mean by idle being bad?

 

why would the rpms drop between shifts???? wouldnt it stay higher because there would be less recipercating weight? i mean wouldnt the crank stay spinning longer if there was less weight to slow it down???

 

There is less momentum to keep the crank spinning from a lighten flywheel. Less mass reduces rotational inertia but also reduces the momentum of the flywheel. The lighten flywheel slows down faster since there is less mass to keep it rotating.

 

It seems like if the crank will be lighter you get more hp and torque. You may lighten the flywheel, but I prefer to begin with lighten pulley.

http://www.unorthodoxracing.com/dyno.html

 

between shifts, you generally let off the gas, the engine begins to slow down b/c it is still pumping air w/o any combustion to generate torque. The pumping losses & friction cause the crank to slow quite rapidly. Any reduction in mass of the reciprocating mass (crank) and rotating mass (flywheel, pulley) would result in a loss of inertia. Inertia keeps things spinning as they are, so reducing inertia results in less resistance to slowing down - the net effect is that rpm falls faster between shifts or anytime you are off the gas.

a lighter flywheel DOES increase torque delivered to the wheels. But it doesn't increase the actual output of the engine, it just allows the power to pass with less parasitic drag. This results in better transient acceleration, i.e. 60-100. but acceleration from a standing start is sometimes hampered. a heavy flywheel has more inertia and thus more momentum once it is in motion versus a lighter flywheel for a given RPM. When you are revving your engine prior to launch, it is beneficial to have more monetum stored in the flywheel at lower RPM, it makes it easier to transfer the momentum to the wheels w/o spinning them. It is trickier to launch a car with a lighter flywheel.

 

You don't lose torque, and you don't gain torque. Prasitic losses due to a heavier flywheel are probably so low that you can't measure the difference on a dyno. Apparently a power difference does show up on a dyno, but that's because of an inherent flaw (some would argue it's a benefit) in the way a dyno measures power. There really is no power/ torque difference.

The car will supposedly be harder to launch though, due to it being easier to bog the engine, I guess.

 

You will lose a good idle which is true. After I installed my clutchmasters flywheel my idle started to flutter a little bite and it still does it but who really cares I get to rev up faster. It is also true that it is harder to launch with it because I'm still having trouble learning and not spinning my tires to much.