ok, so, here's a thought. Read some threads about the possibility of flipping the manifold 180 degrees so that the throttle body faces the front instead of the back of the motor. This could allow extra room for intake piping if you have a dual turbo setup.

 

so...

 

reading up on RHB5s, they say the RHF5 is the replacement for the RHB5, and it's got a max of about 208hp. So, say, the RHB5 turbo is good to 175hp or so. It spools up quickly, and with two of them in series, and being a relatively REALLY cheap turbo, you could grab about 350 or more horses (estimated) from a capable engine.

 

So, have a exhaust shop make up an upipe leading from a stock n/a manifold (say borla or whathaveyou) up to the first turbo, exhaust exiting, enterting next turbo, exiting there and going back down to where the end of the first cat section would be. Intake piping going from the filter to the first turbo, then to the next turbo inlet, then from that outlet to the intake manifold. This would be a great setup, but of course... that's a perfect world where all of our funny little ideas we think are cool would actually happen.

Swapping the manifold around has been done. It's usually to reduce the amount of intercooler piping if you're running a large front mount.

 

Still not sure how much more room you're going to get by doing for a twin setup.

but the interesting part for me is that, the old 80s sube turbos are easy to find, cheap, and would make a great dual setup if you needed alot of boost.

I think the way you're setting up the exhaust wouldnt work too well. The stock setup has a turbo on each bank. it'd be less tubing if you did it this way. Also Something tells me the two turbos combined wouldnt be good for 350. I just think it wouldnt be as cut and dry. But hey, I could be wrong.

My $.02 is that, on first thought, you would need much more sophisticated exahust plumbing.

 

The first turbo would extract pretty much all the exhaust energy that it could, leaving little for downstream turbo. At high exhaust flow rates it would act as a restriction, and the waste gate would be your only real source of exhaust energy.

 

What I think that you would need is a LARGE dedicated wastegate upstream from the first turbo and feeding the second turbo. Both turbos would need dedicated (parallel) intake plumbing and the second one would need a one-way valve in its output.

 

With this amount of complication, I think that what you reall want is a small, fast-spooling turbo combined with larger, higher-flow unit.

 

Might want to google on "biturbo".