The engine for my track car is being assembled and one of the items I need is a flywheel. The car will be used mostly for DE with very little street driving. That being said, I would like to use a lightened flywheel so the engine will rev-up a little quicker, but one of the flywheels (aluminum) I'm looking at weighs only 5 lbs. Is that too light?

The engine is a 2.2 six, not quite stock.

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For the track, I say as light as possible. The only negatives are weakness, some of them break, and it won't idle as smooth.

Idle will be a bitch, especially if you're going to run carbs ...
Andy

My 2 cents,

The positive-
With a lighter flywheel in the 2.2 you will see a faster response time. The engine is already a revver since it's rotating mass is light already due to small pistons.
You should not lose torque. What you will lose is torque storage capacity that you would get with a heavier wheel. You will also have to rev it up a lot more to get it rolling as the heavier wheel stored more inertia. The engine will also wind down faster when depressing the clutch and in between shifts. This will take a little getting used to as you will need to keep the rpms up in between shifts. Heel and toe is the key here.

Think about it-
Personally a 2.2 with a light weight flywheel is fun as hell. I wouldnt go below 10 pounds though otherwise it will not be fun to drive.

The negative-
Going down as low to 5lb has its own issues. Expect to go through clutch dics very frequently as you will be slipping it all the time to get it off the line. Also expect chatter at low rpms. This light of a flywheel is already into sintered iron disc lining territory. Low rpm bog will be noticeable. The older Porsche gearbox's do not like fast shifts. Expect a high rate of syncro and dog gear wear. Not fun to drive unless a track car.

**Edited because I was bad**

12-14 is stock, see patricks 7.2 is as light as I would go.
I have a 9lb with a 2.4 and is just right.

Did you have your 9 lb'er made or was it purchased "off the shelf"?

made, a lightened stocker.

My bad! I still think going too light in a street/ track car is going to take away drivability. 9-10 lbs he should be fine.