I'm getting ready to buy a wastegate for my twin setup and was wondering what size would be right. Not really looking for anything over about 5 to 550 hp. Can a stock wastegate be opened up to handle this without to much backpressure or would I be better off with a seperate gate. I'm running a stock wastegated 12cm 35-40 turbo right now and plan on leaving this for the top turbo with a 22cm bht3e bottom turbo I have already bought. Does the bigger gates have a flutter problem on diesels like a gas motor can have. Can I use the stock wastegate and a small external gate like a 35mm size? Thanks Gary H.

 

The internal only won't be enough to keep your pressures in line nor allow you to keep your boost down if you want it low. You have two options you can go with, and I think they be set up equally well. 1) Run a 35 or 38 mm external in addition to your internal flapper. It requires a little more setup, but when set right they seem to do very well. I run a setup like this. 2) Block off the internal flap and run a larger 42mm external. This is probably easier to tune because you only have 1 to worry about, but IMO you don't have quite the adjustability. It will also cost a fair amount more for a 42 vs. a 38. Hope this helps.

John

 

how well do the internal wastegates keep up when both sides of the snail are opened up?

 

They're better, especially as a single, but they still can't keep up completely for twins. Externals are the way to go.

John