I had mine balanced last week. The flywheel was 20 grams out and the pressure plate was 31 grams out. It made a huge differance. I dont know about hp loss, but it is much smoother.

 

Yes, to both questions. I assume you had a flywheel installed when you put the clutch in. The Spec clutch assemblies come from the factory zero balanced. The LS1/LS6 motors stock are externally balanced. In the front with the harmonic dampner, and if needed in the rear with the flywheel. When installing a new clutch and flywheel, you need to match it's balancing to the old clutch and flywheel, or will get vibration. Essentially what needs to be done is the old PP/FW assembly is run on a balancing machine and it's heavy point is found, then the new PP/FW is lightened on the opposite side by drilling out the new FW in the back untill it matchs the old PP/FW. Then when you install the new PP/FW assembly onto the motor it should balance the motor.

An out of balance rotating assembly puts undue strain on the bearings and crankshaft and at the least will cause higher than normal wear on them. It can also cause higher than normal wear on the connecting rod bearings due to harmonic crankshaft flexing. In the extreme case the bearings or crankshaft can fail, which can be catostrophic.

If you have your old PP/FW assembly, take it to a balancer and have your new PP/FW assembly balanced to the old and you will be fine. If not, you can still balance it by removing the clutch inspection cover and by trial and error add washers under the PP fastener bolts while keeping track by numbering the bolts 1 to 6. It is purely trial and error but you can find the correct comination of one washer here and 2 there, etc. that will yield a pretty vibration-free assembly. It's a nightmare though. Been there, done that. Good luck. :(

 

Well, considering my car makes about 500rwhp on the spray, the LAST thing I need is MORE strain on the bearing and rods!!! Dangit!! I really really don't want to have to pull that clutch out... maybe I will try that washer idea.

 

I felt the same way, but it is definatly worth the piece of mind to take it apart again. You can guess at it with the washer thing, but my pressure plate had to have a piece of steel welded to it in one spot. I know they are supposed to be zero balanced from the factory, but dont trust that. Have your flywheel and pressure plate zero balanced individually.

 

I installed a Spec III 5 or 6 months ago in my 99 C5. It vibrates at certain RPMs, noticeably. Will a clutch that is out of balance cost me horsepower? If so, how much? Even worse, is it possible, since it is out of balance, that it could cause engine damage?

Thanks.