Racing flywheel is good and worth it?

[Frytka]

What its doing? its safe to have it in car?

[Kravity]

Absolutely. It's basically a straight upgrade over the regular one. You'll have less weight and rev faster. Only thing you have to watch out for is that it's less forgiving if you downshift at high speed. Just make sure you shift when you know the engine is not going to overrev, and you'll be fine.

[blueshift1980]

What Kravity said. With either flywheel I would strongly advise against downshifting at or above 5000 rpm.

[Unlucky Mizutsune]

In my opinion, it's a double-edged sword. The reduced weight causes it to stall when moving from stop often, revving the engine when you start it will cause your crankshaft to snap.