What's this hole for - pressure relief? Just noticed air (intake) coming out of it at idle. There's another one on the bottom but it's not venting.

 

It's purpose is to mount a wastegate; it needs to be plugged with a bolt.

 

Those 2 holes are on my SR20 T25 for the stock WGA mounting. One goes all the way through, put a bolt in it to seal it up.

Edit: Brain wins.

 

Thanks. It's been this way since it was first installed. I wonder why Begi didn't plug it or make mention of it in their manual.

 

Wow, you've been running that way since it was installed?
Your turbo has been working hardddddddd to prduce that 8 psi you've been running. You're gonna notice a difference when you plug that hole.
Use a short bolt and put some sealant on it, but not so much that it gets in the housing, just the threads.

 

and turn your MBC down.

 

With it plugged, it definitely has more go. Of course the boost is up almost 1psi - will have to loosen the MBC up.