moespeeds

Will have my C5 FRC up on the lift for a bit, installing an LS6 top end and some other stuff. I might pull the motor, not sure yet. At the very least I'm going to do new motor mounts, should I do stock, poly, or solid? Car is gutted and track only. No street use.

Thanks

davidfarmer

race car, I just cut a piece of aluminum, drill a hole throught it, and mount it solid to the cradle. Yoiu need either front or rear to NOT be solid however (diff).

You can't run knock sensors with solid mounts, it will cause you to pull timing and run in low-octane mode

moespeeds

Thanks Dave. Can you elaborate on the knock sensors? I'm running on 93 pump gas, do I need them? When I get the car tuned after I'm all done will they take care of that? I found solid mounts for $100. I have a lathe and I could easily make them, just use a stock mount to measure off of?

Thanks!

redtopz

It took me about 2 years to figure this out. When I bought my ST2 car it had solid engine mounts (aluminum with a slice of poly sandwiched in there) along with a solid diff mount in back. My diff's kept cracking and leaking. Eventually I realized the rear diff mount was solid and installed a stock rubber diff mount last year. Haven't had a problem since.

sperkins

What about poly on both ends?

moespeeds

The ebay seller who is selling the solid mounts has advised me to get poly instead. I'm sorry, I'm completely ignorant on this whole issue. So what do I want, poly all around or solid front/poly or stock rear? Noise and vibration are not an issue, the car has no interior...

RX-Ben

I had poly-poly and had a leak at the diff/trans junction. Could have been a faulty install (pinched o-ring) - not sure as I swapped out the rear poly a little later (due to a bad trans). I couldn't tell the difference between the poly and OEM trans mount and I am not sure if there is any benefit to going stiffer. I don't think that having compliance back there hurts anything, and making everything solid/very stiff does not seem to be a great idea (no performance advantage and harder on parts, but I could be wrong on this).

sperkins

Before I went with poly engine mounts, I could move my engine side to side by hand a huge amount (150k mile stock mounts). That has to have an affect on handling when there's 400lbs flopping around like that.

RX-Ben

Yes, agreed on the benefits of stiffer motor mounts.

moespeeds

So sold in the front should greatly reduce side to side movement or wag, while leaving stock rear will allow up and down flex for the driveline. Correct?

Paul Schmidt

Ok... Let's get to the bottom of the knock sensor with solid motor mounts. I had Pfadt solid motor mounts on my car. I spun a bearing and bought a Dailey dry sump. I have to have a custom motor mount on the passenger side fabricated. My engine is at the shop right now getting rebuilt and set up for the dry sump. My question is do have them install knock sensors or not. Track only car, so it won't be driven as a daily driver.

davidfarmer

GM Engineering told me the vibration of the engine, normally dampened by the balancer/flywheel/engine mounts would just get overloaded and register false knock. You can either have the low spark table copied over with the high spark table, disconnect the sensors, etc.

I followed GM's advice, so I never actually had the problems they warned me of.

jtmck

Do I understand you can just disconnect the knock sensors or does something else need to be done?

Jim M.

redtopz

I also noticed zero difference between stock rear diff mount and solid mount except that my diff stopped cracking and leaking. The driveline needs some flexibility and ability to expand/contract with temperature fluctuations. It's nice having the engine mounts stiffer and I think most of the the "solid" mounts have some compliance (ie. not 100% aluminum). Mine have a layer of poly sandwiched between 2 pieces of aluminum.

Regarding the knock sensors, I don't have any issues with knock with my motor mounts. I also have my low octane table equal to the high octane. It would be better to leave them connected and deal with false knock in the tune if it's a problem, which it shouldn't be.

davidfarmer

You can just disconnect them in a c5 I'm pretty sure

redtopz

I'm sure you are right. My only point is that if the mounts don't cause false knock then it might be safer to keep them in and use them .

John Shiels

http://www.vbandp.com/C5-Corvettes/C...ount-Each.html

used these with no problem for many miles

redtopz

Those are the ones I have. Work great .

jstout

Great info guys. Thanks for the heads up. getting ready to put mounts in my car. Jerry

moespeeds

Jeez them VBP's ain't cheap! I might go with Pfadts in the front, and stock in the rear. It's hard for me to swallow these prices when I have a mill and lathe sitting here, I could make half this crap. For some reason I'm scared to do it on the car, even though I've been doing it on bikes for years. I guess it's just more $ at stake if I screw something up! That VBP unit would be an easy afternoon if I had one in my hand to copy, and about $20 in materials.