Does anyone know how much the diameter is decreased from the stock crank pulley to an underdrive pulley for our cars?

I know it was said that if you buy an underdrive crank pulley you decrease your stock belt size by 2 inches. I can figure out the diameter using this information fairly easily but it would just be an approximation so I was hoping to get a reasonably exact diameter value.

i'd like to know this too

Anyone know the answer to this??

I was messing around with some math and estimated that the belt was on 2/3 of the stock pulley and assumed it would also be on 2/3 of the underdrive pulley. My calculations revealed that the new diameter should be 5.04"

Anyone know if this is remotely correct?

Outer most lip diameter of the stock pulley is 6 1/2"

The ASP underdrive pulley is indeed 5"

Thanks a lot vsixtoy. Is the outter most lip of the ASP underdrive pulley 5"?

Yes.

thanks a lot