I bought my 64 f85 Cutlass convertible that somebody had swapped a 455 into it already getting it pulled apart and put back together to upgrade and clean things up. One of the items is some Billet pulleys I ordered and the crankshaft pulley that was sent to me is quite a bit smaller than the one that's on there. Do I need to stay with the same diameter as what was on there or can I use the smaller crankshaft pulley. Does the pulley diameter need to stay specific to the motor year?, obviously the smaller pulley is going to turn the water pump and alternator a little slower is it going to be a problem

 

Does your car have A/C? Are you planning to add A/C? I've had two engines in my car with A/C, a '71 350 and I now have a 455 with the pulleys off a 76 Toronado which has the largest crank pulley I've seen. In both cases the the water pump pulley has been smaller than the crank pulley. Both overdrove the water pump 1.4 to 1. Pictures I have seen of non A/C cars shows the water pump pulley larger than the crank pulley so you having a smaller pulley should work if you don't have A/C.

 

You should check the belt alignment with that new pulley. The pulleys from the factory are matched sets for proper accessory speed as well as belt alignment.

 

It is manual steering and no AC. Only crankshaft water pump and alternator

 

The whole point of the billet pulleys is that the smaller crank pulley diameter reduces belt speed, which reduces accessory speed which reduces parasitic HP loss. Of course, turning the alternator slower reduces charging. Turning the PS pump slower reduces steering assist. Turning the water pump more slowly may reduce cooling at idle. Your call on whether or not you want to put up with that hassle for an additional 2 or 3 HP at wide open throttle.

 

The cheap sets have the tiny, very under driven crank pulley. March and CVF Performance have less under driven options.

 

OK, so the task is cut in half. You only need to verify that the crank pulley lines up with the water pump and alternator pulleys.