engine harshness at high revs

Scribe

Likely this has to more to do with the natural imbalance of the V6, which has been exacerbated as they stroked the original VQ engine design more and more. Another engine recently revised with a longer stroke and VVEL is the VK50DE. How harsh is the VK50 in the FX50 at high rpms?

Edit: After finding Edmunds review, they stated that the VK50, 'much like VQ35/37 this V8 isn't quiet or smooth @ high RPM.' So we can rule that it's either the longer stroke, the VVEL or both.

VTalumni

So, the problem must be related to the engine since it is noticeable in both the 6MT and 7AM (I know more in the 6MT but that doesnt matter).

Was this problem noticed in the 350z? Someone mentioned the VQ35DE was smooth. I am not familiar with engine names, but is that the 350z engine?

To me, the problem seems like its related to the VVEL. Do the vibrations increase gradually as you rev higher or is it an instant thing? Has anyone driven a Honda with VTEC? VTEC kicks in full force at a certain rpm. Its like a whole nother engine. The intake seems 17 times louder than before VTEC kicks in and the whole car becomes harsher. Does it seem something like that? If so and the vibrations really kick in all at once at a certain rpm, then we can confirm that it is something related to the VVEL. If not, maybe it is an imbalance in the crankshaft or camshaft, something rotating.

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m4a1mustang

It's really a gradual thing. It gets worse as you go up in revs. It's nothing like the VTEC transition where at a given RPM *bam* you have a new engine.

VVEL may or may not have something to do with it, but I'd venture to guess that it probably isn't the root cause. It's probably just how the engine naturally behaves and we just have to deal with it. It's definitely wierd, though, because it doesn't feel right when you drive the car hard... but it probably is right. Just have to get used to it I guess.

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6SPD_FTW

The electronically controlled motor mounts are usually 'soft' at <950rpm and
'hard' at >950rpm. The VQ35DE in the Altima/Maxima/Murano has a vacuum/solenoid controlled system that softens the mounts at idle and hardens them at speed. The 370Z doesn't have this system. There's vacuum tubes that lead to the motor mounts that would be there and they aren't on the Z.

Dunno bout fluid-filled mounts, though. Nissan used fluid-filled mounts on the transmission and front (side) motor mount on the Altima VQ. Judging by the harshness of the Z, I'd doubt there are any fluid-filled mounts on this car.

Late,
Trav

turbo8765

It's largely an inherent property of the engine. A V6 is not inherently balanced. Neither is an inline 4 cyl, a boxer 4 cyl is.

Straight 6 cyl and 90 degree v8s are inherently balanced also. That's partly why BMW uses straight sixes and refers to a V6 as a bent six.

When u take a motor that's not inherently balanced and give it large pistons and a long stroke (high velocity), it's going to vibrate a lot. You must then add counter weights to smooth things out, but that robs power and increases complexity. They can be made smooth ie NSX, but it's not easy.

I have an M3 and a 335, and they're smoth as silk. Coming from that, the VQ37 feels VERY harsh.

You can't compare the vq37 to the v8 because the v8 is an inherently balanced configuration.

I could explain in much more detail, but I'm typing on my iPhone

turbo8765

It has nothing to do with VVEL.

Scribe

That was my theory, but the V8 "version" of our engine is also rough in the high revs. That's what my post pointed to, but it's got to be something else or the VK50 would be smooth and apparently it's not.