S5 stock maniold, external dump

[sen2two]

38mm is plenty large enough. My motor is completely factory. Hasn't even been rebuilt yet... Most people port the stock wastegate to 35mm.

I am not a fan of overly large wastegates. Here's why... In theory of course, but I would rather be safe than sorry in this case.

whether you have a large wastegate or small wastegate, they still open at the same speed. And that speed is quick. When you hit your set PSI and your overly large wastegate opens, it releases a large amount of exhaust pressure quickly. Most of the time TOO quickly. Causing exhaust pressure drop and possibly a drop in boost momentarily slamming it shut again only to open quickly again. You might not notice this, but I'm sure the motor does.