How balanced is the 370z's engine?

6SPD_FTW

Well, that's the thing. It's not an issue of balance. Every crankshaft is perfectly balanced as is. That's not the issue. Yes, even with an aftermarket pulley, it is still balanced. You could spin the crankshaft up to 7500rpms BY ITSELF with the stock harmonic damper and with an aftermarket crank pulley and everything is still balanced perfectly. However, when you start applying force to the crankshaft (like the power stroke of 6 cylinders every 120º of rotation), it becomes a very different story. A harmonic damper has a rubber/polyurethane ring that seals an inner race to the outter pulley, which absorbs flexion of the crankshaft. The crank is flexible and absorbs quite a bit of the impact on each power stroke. It twists and deforms slightly on each and every power stroke. There are certain rpms (harmonic frequencies) where that flexion is much worse than others. When the force from that power stroke is removed at the end of the burn, the crank resumes its normal form. The harmonic damper is what keeps the crank from releasing all that energy so violently and suddenly. The crankshaft "snaps" back into its normal shape as the energy from the power stroke is released. Ergo, installing an aftermarket pulley without the harmonic damper will possibly increase bearing wear as the crankshaft has nothing to prevent that sudden release of energy after each power stroke is complete.

That's the theory, at least. Some engines do just fine, some self-destruct. The 2ZZ-GE engines on the Celica GT-S/Matrix XRS/Corolla XRS tend to eat oil pumps because the oil pump couldn't handle the shock of each power stroke beating it to death (oil pump driven directly from the crank). Just an example (catastrophic engine failure, to be sure). I'm leaving mine alone. It's up to you. The VQ37HR may do just fine, but then again...it may not. No way of knowing til its too late, maybe.

Late,
Trav