[A Snake]

As usual, Mr. Fixit hit it right on the head, without mincing words.

The lighter the better is true up to a point. If the engine will idle is part of it. What this means in plain english is, the same cam will idle rougher with a light flywheel than with a heavy one, because of the dampening effect of the extra weight. Simple. It takes more energy to move more weight. Therefore, the crankshaft rotation is not disturbed (slowed down and speeded up) by the misfires caused by a lumpy cam.

Now, with that said, the other part is plain old driveability. Simply put, the higher the gear ratio, the more flywheel weight is needed for the car to move without the engine stalling when the clutch is let out.

Summation. 427 in 2,300# car 3.xx rear gears, 20-25# for street, 15-20# for track. An ultra light flywheel is great for throttle response, but miserable to drive on the street in traffic.....even in a light car like a Cobra.

In my case, I used billet steel on the advice of my engine builder who is also a pro racer. It was machined down from 40# to 25# and worked well on the street as well as the track with my 427 S/O and top loader with 3.54 gears.

I was warned NOT to go with aluminum as they have a nasty habit of coming apart on a bad day. On a good day, they will warp more quickly, because there is a difference in heat transfer from the steel insert to the aluminum disk.

What no one should EVER DO is use a stock cast iron flywheel in anything but a stock pickup. NOT EVER in a Cobra or other high performance car.

By the way, going from 3.54 to 3.31 won't make any appreciable difference in gas mileage, but it will make the car feel a little soggy at lower rpm's. I went from 3.73 down to 3.54 and was delighted. The car was plenty perky and much more driveable. Frankly, I wouldn't go to 3.31 from 3.54. I got real close to pegging my 180MPH speedo with the 3.54's. That was God's plenty for me!

Try the 25# steel flywheel. I really think you'll like it.

Al