It really depends on a couple of things; First, is it a quality part or is it a used burned up piece of s**t. (I've been screwed a couple of times trying to find good flywheels for my dirt modifed.) Second - what are you going to use it in? With a light car, i would be OK, but in a heavy car ('40 and on), it's probably not a very good idea.
TubMan has it about right: I depends on the complete engine, trans, rear, tire and car package. The main thing about lightweight flywheels is that they don't store much energy, so they have less to transfer to help a car get away from a stop sign (dead stop). So . . . if you have a heavy car or one with tall rear end gears, big tires or maybe a Zephry geared 39 box, then you'll need to slip the clutch a bunch more to get the car moving. The Pros --> on a light car with low rear end gears, and a bigger cubed stroker motor, they are fun! They sound great with a big cam, really rev fast, etc.. I ran a Schiefer for about 4 years on the street -- in a 34 Ford sedan. I had 4.11 gears, Zephyr 25 tooth 39 box, etc.. I ran a 10" cluthch. The motor was 284 cubes. I had no problems with it, but I did slip the clutch more than you would with a heavier flywheel. I think I would have liked a steel billet 25 lb one more in retrospect. Another option is to have a stocker cut down or buy a steel flywheel from McLeod (I think they make a flathead one in the 25 lb range???). Also, maybe talk to Pat at Wilcap. I'd explore my options for a good steel one - if you can find something in the 20 - 25 lb range, you'll probably actually like it a whole lot better than an aluminum 12 lb flywheel. Best of luck!
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