How balanced is the 370z's engine?
 

Looking around the forums I see some discussion and modifications of the pulleys which sounds all well and good, but by changing it to a light weight pulley how unbalanced does the engine become? If the engine wasn't very well balanced to begin with, and then you throw a much lighter pulley on it, that's just asking for trouble and longevity issues. So in short does anyone know how balanced the Z engine really is?

ps. Yes I definitely meant to type "how WELL balanced is the 370z's engine?" as the title for all you english geeks out there ;)

you can change the thread title in advanced settings

there has been discussion on this topic aplenty... if i recall correctly, the consensus is that the various pulley options are so minimal relative to the mass of the other spinning parts of the engine that even if nissan had engineered in an asymmetric weight distribution in the stock pulley and if the aftermarket pulleys were different, it would have ZERO negative impact on the balance of the engine.

The pulley rotates on a fixed axis and is a perfectly balanced circular piece....it would not throw off any balance that you speak of...

anyway our 6 cylinders engine should be much better than ANY 4 cylinders engine..

It's not the centrifugal force being unbalanced that's the problem. If the stock pulley is actually a harmonic balancer (which prevents abnormal crankshaft flexion) and you remove that harmonic balancer, then you may end up with some abnormal crankshaft flexion and worn out main bearings. The harmonic balancer absorbs some of the impact of each and every power stroke. Just sayin....

And would you say a lightweight pulley(s) would unbalance this?

I have yet to see a true power benefit from pulleys, done here in our shop..same day...same car.

I tend to prefer the OEM pulley, or something like a ATI Damper, rather than the lightweight aluminum machined pulleys. I have seen instances where the crank pulley and keyway on the crank shaft attacked each other, and destroyed the crankshaft. Not worth the risk, IMHO. Stick with stock, or hi end motorsports fluid type damper.

Thanks for the imput Sharif! Yeah I was worried that something like that might happen.

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

Thanks for the clarification and great description! Yeah I agree it's not worth the risk, at least until a few years down the road where we see how the 2009 370Z's that now have cranks are doing with a lot of miles on them. It wouldn't be too smart destroying a whole motor just for a lightweight pulley(s).

One more question though, I know it's been clarified that the lightweight clutches don't effect the rev matching feature on the sport package. But how much quicker does the engine rev with a lightweight flywheel/clutch and the pulley(s) compared to just a lightweight flywheel/clutch? I know there hasn't been a lot of people doing pulley's and I haven't seen anyone with a lightweight flywheel yet but I'm hoping that someone out there does so we can compare to stock, and to just doing the flywheel/clutch.

i have the JWT flywheel, JWT clutch and stillen under driven pulley... pulley was installed first. Big difference in responsiveness of throttle with flywheel... engine now slows quickly enough on up shifts that I can shift very fast without being at too high an rpm on up shift... sorry, can't tell you if there is a difference going from lw clutch/flywheel to same + UD pulley... did it in reverse order, but honestly I have to guess that the UD pulley made very little difference... i did the UD pulley more for the HP gain... more details in my journal

No kidding. There's better mods you could do for 2whp than a lightweight pulley.

every bit counts when your tweaking a na motor, mixitup