I'm putting a b20 in and Im wondering if I should use the B20 crank pulley. Im just using an altrernator, and the B20 crank has a bigger diameter on the crank circle, so it would slow down the alternator compared to a B18B pulley right?

 

uh , bigger pully would mean that it would spin FASTER, i'm using the b20 pully on my swap now and i THINK it's been fine, i had the battery dead a few time on me before but i don't THINKG it's alternator related. it works i can tell u that, will it kill your alternator, hopefully now, hehe, you need the get a B20 belt though, the ls doesn't fit, cost freakin $10! hahaha