Why does my car vibrate whenever i engage the clutch???
 

Only when I am starting in first gear or reverse... I have a poly tranny mount could that be the problem??? It's like when I start it's good good good then as I let the clutch out more it shakes. It felt like when I had my stage 3 ceramic in there but now it's just a stock disc with an LT4 pressure plate. How many times can you resurface a flywheel before it hits min. thickness??? Could that be it?

If you've had an intake or rear main seal leak and oil has gotten on the clutch disk, it can cause the clutch chatter you describe.

Its known as chatter or "body boom." If its chatter, it could be caused by oil on your disc as nateh mentioned, or the newness of the disc if its new. Do you have an actual OE replacement, or a cheaper aftermarket "OE comparison" The aftermarket ones probably don't filter the vibrations as well as OE does, which would result in body boom. Body boom is simply resonance that isn't properly filtered out through the dampers and pre-dampers of the disc. If it is an OE disc, you could have a broken spring (depending on how long you've had it and how much power you make and how you drive it). Even with my stock disc, I would get a little vibration on engagement. Just play with the clutch and gas pedal as you take off to avoid that point, since it probably only occurs in one small RPM range. I'd check for oil leaks too. Why did you switch from a SPEC to OE?

I just put in a star spec stage 3 with their lightweight flywheel, i know its new but BOY does it make alot of noise with the console off :D