i was looking at the back of a turbonetics turbo i recently purchased and was wondering why there is a hole cast into the exhaust housing. i would think that the hole would slow spool by causing a disruption in flow. can someone fill me in on the reason for this being there. it doesn't look like it has anything to do with an internal wastegate.

 

its designed for setups that use an internal wastegate. When the manifold is cast, it has that portion in the mold, and if its used, the metal is machined out etc..

 

but for internal wastegate'ed turbo the five bolt flange is raised. plus it does not have the second hole for the wastegate actuator.

 

I'm guessing if you're using an external wastegate you are meant to cap that hole with the downpipe flange.

Dodgy manufacturing if you ask me.

 

You can:

A) Use the swing valve assy and go internal WG.

B) Block off the hole with a one hole flange.

C) Port up the WG hole even more and make your own special flange with DP flange and external WG flange.

Option C is great for people using OEM manifolds without hole for external WG (like Volvo).