David Floyd

With boost set at 10 psi, car seems as fast now as 16 psi was before the rebuild ( Huntley stage 4 MAF and stage 2 turbo ) Should be alot of fun when I can turn up the boost.

I had been chasing some oil leaks that turned out to be some of the bolt holes for the upper and lower balance shafts covers, some of these bolt holes are deep enough to allow oil to stream out, with these capped off, oil leaks are gone.

I do have one problem with a vibration at 2800-3100 rpm's, it is rather pronounced, I first thought that I made a mistake in choosing to delete the balance shafts, but after talking with Tim, the deleted shafts are not the problem. The engine is smooth while sitting still and revving to the problem rpm range, it only does it while moving, if I drive at the problem range in any gear and make a turn to the left the vibration stops and as soon as I straighten up vibs return.

I have rechecked the torque on all the bolts I can think of and everything is tight.

I know an alignment needs to be done, but the car drives ok, seems to be a little extra neg camber on the left front where the vibs seem to be comming from.

Everthing is new or rebuilt.

Anybody got any ideas on what to check ?

Ski

Bad motor mount on the left side?

David Floyd

Maybe, but it's new and no leakage.

Anyway to check a motor mount ?

CPTdooberhead

Get it on a lift and do a visual check...then measure em.

Matt O.

David just wanted to say congrats on getting your beast boosted! Good luck!

-Matt

MAS

I was under the impression (perhaps mistakenly) that the balance shafts cancelled out vibrations at more than just the idling speed. It doesn't surprise me that there would be other points in the rev range when you would get greater vibration. I think that Ferrari had this problem with the old 3 litre four cylinder engines they used years ago.

-MAS

David Floyd

[quote]I was under the impression (perhaps mistakenly) that the balance shafts cancelled out vibrations at more than just the idling speed. It doesn't surprise me that there would be other points in the rev range when you would get greater vibration. I think that Ferrari had this problem with the old 3 litre four cylinder engines they used years ago.
-MAS

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Maybe, but if it was a balance shaft problem, would it not also vibrate while sitting still and revving the engine ? it only does it while moving.

MAS

"... Maybe, but if it was a balance shaft problem, would it not also vibrate while sitting still and revving the engine ? it only does it while moving."

[I'm no expert here, but...]

Not necessarily. Any reciprocating mass (like this moddified engine) will have certain points/speeds/rpms when it will vibrate more than others. An engine like this will have different characteristics than a stock one. It may well be that your engine would vibrate badly at idle, if the idle was low enough (ie: about 500 rpms). The whole engine would have a different "resonance" than a stock one.

-MAS

IceShark

David, you have a key difference being the engine is under load rather than free wheeling. You can cause some pretty good vibrations, though in my experience it has been inadequate mounting that was letting matters get out of hand to the point things were getting torn up.

So I wouldn't rule out possible causes just because you can free wheel the engine without vibration.

David Floyd

MAS & Iceshark, good points, so why when I drive in the problem rpm range and turn to the left the car smooths out and as soon as I go back straight vibs are back ? The vibs also change with bumps in the road, I also should note the vibs are bad enough to be audible.

I talk with Tim about the balance shafts because that was my first guess, he assured me that was most likly not the problem as he has been in several cars without the shafts and no problems with vibs.

Nothing possible with be ruled out untill I can find the cause

TurboTim

I drove in Tony Garcias car yesterday and he has no balance shafts. Car felt good with no annoying vibrations at any rpm. Ok..... actually the car felt real strong. Amazing for a 2.5L. I would bet that he is putting out close to 375 at the wheels at 17 psi.

IceShark

I don't know enough about the mechanics, David. But it could have something to do with mass shift; and the engine is asymetric.

Do you have a LSD?

Ski

David, I would measure the new motor mounts just to rule them out. Can you feel any of this vibration through the shift ****?

David Floyd

Iceshark, I do not have LSD

Ski, vibs not thru shift ****. What am I to look for when measuring the mounts ?

Luke

did anybody touch your flywheel? If the shifter shakes it's ususally a flywheel issue. Where as dash board shakes are motor mounts