Ok here's what I think I know...external wastegates bleed away excess boost. so if you're only boosting 10psi and your turbo spools and puts out 15, your wastegates routes 5psi into the dumptupe which goes into the exhaust/atmosphere. Also, if you have a 5psi spring inside your wastegate, then the lowest your can boost is 5psi?? I know that doesn't sound right, someone please correct me.

Anyway, I need to know what's the difference between the 38, 44, and 48mm Tial wastegates. 48 sounds like overkill for my goals, but I'm worried that 38mm might be too small. I'm not sure if the size is supposed to correspond with the amount of HP your making/aiming for or what. For additional info...

Goals - 350hp on a b16 with room to get to 400 if possible, BROAD TQ band. have no idea which turbo yet. i don't know if that's neccessary info but if you need anymore let me know.