this "555's are good to 600RWHP" is a myth that came from a post of mine a while back in the Technical forum and was taken incorrectly. 720's can flow 600RWHP and that's an upgrade! 555's will max out at about 500RWHP give or take a few HP. 555's should have been our stock sized injectors if Nissan knew what they were doing. Supra's put down massive HP from a simple formula... big turbo(s) + big fuel system = big HP (anywhere from 600 RWHP up to 900 RWHP). I am convinced the Z could do the same but nobody's done it cause everyone here is so hung up on 555 injectors thinking that they're big enough... if you want to compete with the big boys then you gotta go big. Just wait until Mike H. (Phoenix) gets his Z done... it's gonna be a shock to everyone here... he know's what Im talking about... he knows the formula for HP and he's not playing around.