Im thinking about gettin a 3" turboback for my 1jz sc300...plan on going big single later on the road and wanna make 500whp+. How much do you think the 3" will restrict at those HP levels? Or should i opt for a 3.5 or 4"

 

Coming from a Single'd Supra with a 71GTQ I ran a 4" all the way through. At 500-550 the gains from a 3" to a 4" are minimal. The spool increase would be fairly nice, but the cost might not be. For that kind of power I would opt for a cheaper 3" setup than expensive 4". Also, remember, less restrictions in a turbo setup = always better