[Bob Bidonde]

The flywheel plays an important role in the dynamic response to the engine's vibrations. When the flywheel & clutch are lightened, the consequences are:
1. Lightening the flywheel & clutch reduces main bearing stresses;
2. Engine acceleration and car braking are improved when the flywheel & clutch are lightened. Torsional impulse stresses in the crankshaft are also reduced. Fuel economy should be a tad better;
3. The flywheel is a gyro that when spinning, it resists changes in its position, especially rotation about the rear engine mounts. Thus its vibration damping quality is reduced when it is lightened;
4. Imagine that the rear engine mounts are the pivot in a seesaw. The engine is on one side of the pivot and the flywheel & clutch are on the other. Vertical vibrations of the engine will be less dampened (more severe) when the flywheel & clutch are lightened. Clutch chatter may become an issue, but in my experience, tightening the front engine support can tune out the chatter.
In short, there are positive & negative consequences to lightening the flywheel and clutch. Personally, I like the positives more than the negatives, so I did it.