Just trying to figure out what the difference in the uses are for a 4 groove or 3 groove crankshaft pully are???

I have a 440 with stock altenator, cast iron crank with stock balancer, will have A/C & PS..... Why would I need a 4 groove crankshaft pulley?? or why not?? Could I just use a 3 groove?

planning on buying an aluminum pulley pictured.....

7146104-3groove.jpg (63 downloads)

Finally Done....BEERS!!!