If you go over I would say 300 hp, your gonna need to do atleast a valvebody upgrade. If you go over 350, then you might wanna consider talking to Level 10, or PFS about a race built tranny. And as far as it goes, the autos are stronger than the manuals anyway. But once you decide you want more than I would say 500 rwhp, than aftermarket custom is the only real option other than the Getrag V160. I'm getting ready to build a full race car, so at first I was thinking V160, but if I go 1/4 mile drag build, then I'm just gonna put a powerglide on it and run it like that. We are mapping out a semi tube frame, with a locked in roll cage that connects directly to the rearend. So when we finish, it will have a Toyota 2JZ, and "look " like an IS 300, but behind the motor and under the shell will be a completely different story.