Ok.
Some people will argue that a heavier fly wheel is needed for drag racing. Having a lite fly wheel will lose momentum between shifts bringing your RPMS to low. Some of the LT1 tech threads over the years showed some guys running slower with lite weight fly wheel. Whether this was the actual cause or not who knows.

Now having a liter fly wheel will decrease rotational mass allowing more power to be transfer to the ground...

So when it comes down to it which is actually better for drag racing. Assume that your transmission shifts fine.
Compare M6 to A4 or if it matters.

 

you want a lighter flywheel, it free up rotational mass and allow the engine to rev faster

 

Optimal weight for the flywheel is going to vary with the combo. My heavy M6 car (previous setup) had a lot of trouble getting out of the hole, even with over 700rwhp. I am convinced that it would have been easier to get a strong, consisten launch if I had a steel flywheel. If I had continued with the M6, I would have switched to one. I finally had to spray out of the whole to get it to launch hard.

Having stored rotational energy in a flywheel/flexplate is much less of an issue with an automatic. A typical automatic multiplies torque between 2-2.5X at stall. That's why flexplates are so light compared to flywheels for manual trannys. They can just adjust launch torque by varying launch rpm. So for an automatic, lighter is probalby better. For a manual car, it will depend on the weight of the car, the gearing, and the torque curve of the engine. Most serious production based drag cars with manual transmission use heavy flywheels.

Rich Krause

 

The heavier Flywheel will store energy for the launch. Problem is it iw not rev as quick eating HP but will also keep your RPMs up on a shift.

Auto matic guys that are real serious like a heavier flywheel also. it does nto help on the launch as much as it does on the shifts where it helps the motor pull though the lower RPM area by keeping RPMs up.

Much like a lite Flywheel is harder to drive on the street and tends to be harder to launch a liter Converter and flexplate give up the rotional pull you had built up.

For road racing the Lite combo's are king as you are always going up and down the RPM range and need all you can get. In drag racing and even street duty a heavier combo pays divedins by keeping the motor spinning.

Anyone ever install an aluminum Fly wheels on a street car? Ever notice how it felt like it surged more and teneded to bog or try and kill the motor more as you tried to slowly pull away froma light? A heavier fly wheel keeps the motor spinning

Many 96- cars have also had problems with lighter converters with an automatic. They do not have the rotational mass to keep the motor spinning at the desired IAC settings. Most notice the car surging at idle and fighting to stay running.

My new motor will be running a CSI billet Flywheel in front of my Yank 9in converter

they both have there place. pick which atribute you would like the most

 

Rotational Inertia is your friend when launching a 3700# Fbody. If I dead hook I'll bog even with a steel flywheel , a street twin , and 4.10 gears with lil 26" tall tires. That being said, I hardly ever dead hook. I little tire spin on an M6 car is a good thing.

Dead Hook = Broken Pieces Parts

Steve

 

Muscle Mustang and Fast Fords did a very in depth review on lightweight flywheels, and it was determined that in every case, i.e. close to stock, moderately modded, and highly modded, that a LIGHTWEIGHT flywheel was beneficial in every case. Any launch problems could be solved by better tires or better driver. The slight benefit that the heavy flywheel had on the launch did not make up for the loss in the shifts. I need to dig that issue up. Excellent tech info in MMFF.