That's bull crap. Tell him to explain to you how a lighter flywheel will reduce the torque output of an engine. If heavier is better, why isn't the flywheel 40lbs, 50lbs?

A lighter flywheel allows the torque of the engine to accelerate the car more efficiently. Remember that everything the crankshaft is bolted to has to accelerate, as well as the car. Since the flywheel spins from 800rpm up to 6400rpm (in the case of your 535), it is the fastest spinning thing in the drivetrain in 1st, 2nd, and 3rd gears. It takes power to accelerate the flywheel, so why not reduce the mass? From pyhsics remember that Force (F) = Mass (M) x Acceleration (A). This converts to F/M = A. To increase A, you have to reduce M or increase F. Increasing F is the same as getting more torque from your engine. Reducing M is easy--buy a lightened flywheel.

You can also buy a lighter clutch (expensive) and lighter wheels. The wheels spin slower than the engine/flywheel, so they don't affect acceleration as much, but it is noticeable! Put 14" wheels and tires on your car do a few runs from 5-100MPH, then swap for 17" wheels and tires and run again. Starting at 5MPH reduces the chances of wheelspin screwing up your numbers. You'll notice a big difference.

Your mechanic friend has no idea what he's talking about. The only bad thing about a lighter flywheel is it will make the idle a little more harsh. The heaver flywheel smooths out the idle. Above 1000rpm it doesn't do any good. You may not even notice it.

I've done it in an E30 M3. Talk about a kick in the pants!! It makes the biggest improvements in first through third, but there is still a noticeable gain in fourth and fifth gears. The idle didn't suffer at all, either.

Your friend has been horribly misinformed.

James
james_535@yahoo.com
88 M5
88 M3