custom tune is the best. i made the noob mistake and slapped a 3.4 pulley on my gen II and it eventually blew up. i had no tune and i could tell it was pullin timing. after about 6 months (many short trips) i threw a rod right through the block. dont just drop pulley size. do some alot of research and get supporting mods before slapping a smaller pulley on it. dont make the mistake i did.