Steering Vibration At High Rpm

[Littlehorn]

HI guys i have a 96 R33 gtst race car.

I have been getting a vibration at speed for a little while which has increased recently and is now a real worry to me.

Car has a nismo 2way lsd, solid subframe bushes, super pro front diff bushes. Car also hasnt been tuned running exhaust filter front mount and 10psi ebc (Going in for tune next week)

Symptoms:

Vibration is through the steering wheel and dash when i get into 4th.

1st and 2nd gear no vibration at any speed/rpm.

3rd gear vibration from ~5500rpm 125-130kmph

4th gear vibration from ~5500rpm 160kmph (Vibration is much heavier than in 3rd the whole dash feels like it is shaking up and down)

Haven't managed to test 5500rpm in 5th gear as i run out of track but im assuming it would be the same problem.

Things i have checked

- Drive shaft u joints all look/feel good and are in alignment.

- Steering rack has no play

- Wheel bearings appear fine

- Wheels have been thoroughly checked and they are in balance.

- Car has been aligned

Any ideas on what this could be?

[GTSBoy]

If it is at the same engine rpm in different gears, it implies it is not behind the gearbox or the wheels. Makes it sound like input shaft. Somehow.

[Littlehorn]

The transmission is actually new (second hand reconditioned). I had the same vibration before it was replaced.

The other possibility is the gearbox mounting bush which is still standard not sure how squishy this should be. Or the engine mounts which are standard but i have no idea how to test there is little to no movement when i try to move engine by hand.

[Jazzadub]

From your description it sounds like it is crankshaft speed related, so I agree with GTSBoy that it is not related to the transmission or axles.

I think you need to urgently check out your harmonic damper and flywheel to see if they are in good condition as if they are not working or out of balance your engine will probably not last much longer.

I would also check out all engine mounts, as they may be worn, and not able to dampen the vibrations occurring at 5500RPM.

[Littlehorn]

I changed the timing belt not long ago harmonic balancer appeared all good.

Could the vibration be caused by a misfire only occuring at high rpms?

[GTSBoy]

It could be. There is more load in 3rd and 4th than in the lower gears, so maybe it's missing there and not missing in 1st and 2nd.

[Littlehorn]

I will check tonight but im pretty sure i get no vibration in neutral which i guess would rule out flywheel imbalance, and mean the problem lies somewhere from crankshaft forward.

If the engine mounts are bad i would guess that i would get little vibration in neutral as there is no load on the engine correct?

Other reason why i am suspecting possible tune issue has increased the vibration is that i have recently installed a new steel wheel turbo HRC internals in stock mounting position. Which may be aggravating the problem.

Going in next wednesday to get a link installed and tune with someone who knows what they are doing, he will also be replacing the plugs and gaping them himself.

[GTSBoy]

OK, so you're running a bigger turbo (I assume it's been highflowed if any money/effort has been spent on it at all) at 10psi on an untuned ECU?

Do you know what R&R feels like?

[Littlehorn]

I was running 10psi before turbo. Since the turbo was highflowed It has been running 8psi.

Reason i am getting tuned is it felt weaker after the turbo install.

But i did have the vibration before the turbo install.

Edited March 12, 2014 by Littlehorn

[Littlehorn]

Here is a pic of my engine mounts, anyone know if this is normal?

[Littlehorn]

There is no vibration at 5500rpm in neutral.