the difference between big and small shaft compressor wheels is 1/16".. it may not be slipping after you tighten the nut, but the difference is enough to put it way off balance, slowing rotation (spool) and the wheel is probably rubbing the housing making the howling noise

 

Yeah, I rebuilt the turbo, replacing all seals and bearings when I built the hybrid, so the side to side play was very minimal. Someone was saying that the gasket in the exhaust could vibrate producing a whining sound like a reef on a saxophone if the exhaust bolts were loose. I haven't pressure tested anything yet if that's what you mean by testing for boost leaks. I hope it's not the compressor wheel touching the housing. I figured it would grenade itself if that ever happened

 

Perhaps you compressor wheel is not matched to your compressor housing. It may not have a tight enough clearance greatly reducing its ability to create pressure/boost.

 

Well the compressor wheel and housing came off of another turbo. So they were meant to go together if that is what you mean

 

On a side note my compressor wheel dimensions are "Compressor Wheel
Exducer: 69.31mm, Inducer: 53.90mm". I can't find anything like this. Is this a 57 trim? 60 trim? I know the dimensions but nothing else and I can't find another wheel with the same dimensions

 

nobody?

 

T04b U Trim is 54/70mm

 

probably a V-trim

Compressor Wheels & Housings

 

V Trim is 55/70mm