I have an 86 gt and i want to swap my stock pulley for an aftermarket one and im only swaping my crank only and leaving the other ones stock, My question is do i need to change my belt for a smaller one or do i just use the stock one.THANKS FOR YOUR HELP.

 

smaller pulley = smaller belt...unless the car has tensioner.

 

you can try it but most likely you'll need a shorter belt