[tbone17]

Does anyone have any experience with polyurethane motor mounts in a LT1 car? A customer brought in a 95 Trans Am that has a significant vibration at 2500 rpm the motor seems to run ok, but it has poly mounts in it, and I was wondering how smooth these cars are with these mounts in normally. Any thoughts?

This post has been edited by tbone17: Apr 20 2015, 06:49 PM

[Blainefab]

Does anyone have any experience with polyurethane motor mounts in a LT1 car? A customer brought in a 95 Trans Am that has a significant vibration at 2500 rpm the motor seems to run ok, but it has poly mounts in it, and I was wondering how smooth these cars are with these mounts in normally. Any thoughts?

I've run poly in the motor and trans - maybe a little more high frequency buzz gets into the cabin but nothing that RPM specific - I'd look elsewhere. A couple thoughts:

The OEM damper rubber can fail and start to separate
has the clutch been changed recently? OEM LT1 is externally balanced with an off balance flywheel
check the bellhousing for cracks - the upper bolt bosses can crack off
check plug wire routing from opti to plugs - swap a pair of cyls and it will run but not right

[CrashTestDummy]

[<SNIP>
check plug wire routing from opti to plugs - swap a pair of cyls and it will run but not right

I'd think you could quickly determine if you have any plug wires crossed with an IR thermometer. Start the car, and point it at the individual primary exhaust tubes. Any mis-firing cylinders would warm much slower than the others. I'd expect crossed wires to show up worse at idle than just about any off idle RPM.