I just started posting on this board, but there is a guy I know from another board who is working on producing both intercooled and non intercooled turbo kits for the E28, and M30 & M20 motors in general. He drives a euro 535 and put the turbo on his stock motor. No build up of his motor or anything....just put the turbo on and drives it. He runs like 14-16psi daily and pushes the motor as hard as he can. His stage one kit (tuned properly) can achieve 475 rwhp. Now I know that sounds like a lot, but read his website and see what you think. I can tell you that I fully plan to put his kit onto my car within the next 6 months. Anyways, go to his site and read about it. Turbo Charging Dynamics
I hope that is something along the lines of what you are looking for.
<img src='http://home.comcast.net/~evanswink/bremerton-9.JPG' border='0' alt='user posted image' />
1987 BMW 535iS
BBS RS with Yoko AVS ES100
BavAuto lowering springs/ Koni Yellows
B&B Tri-Flow exhaust
MOMO, Alpina, Factory ///Motorsports, Alpine, JBL, JL audio goodies on the interior.
TONS of cash everywhere HA!
<a href='http://www.cardomain.com/id/fastfiver' target='_blank'>Check out my ride on Cardomain!</a>
"I don't drive fast, I fly low!"