Just curious.
I was looking on ebay and a Garrett GT42 is like $296 BIN and they're stating it is the right size for a RX7 or Supra. I'm not sure of the size of the RX7 engine, but the Supra has a 3.0, so although it'd be a little bit small it states that the turbo is good for 650 HP in a RX7. I'm curious if this turbo could be good for 400 in the 3800.
If not what would?

A GT42 is a LARGE turbo. If you're looking for a car to drive on the street you don't want a GT42. On ATP'* site their GT42R'* have 850hp and 1000hp turbine options. You should be looking at GT35 and smaller turbo'*. For a 3800 powered car I think I'd probably go GT3076R for a 400hp application but thats just me.

http://www.atpturbo.com/Merchant2/me...egory_Code=GRT

It is a $2300 turbo though.

There'* a dude with an XR4Ti, and he mounted a Caterpillar diesel turbo he found...

That would take eons to spool... unless it was from some tiny skid steer, but it'* still not a great idea.

The fastest way to get an answer would be to find out what the Buick Grand Nationals are running.

An other option is go get Corky Bell'* book. It will explain housing designs, trims, how to read compressor maps...

A friend of mine sized his turbo using this calculator:
http://www.not2fast.com/turbo/glossary/turbo_calc.shtml

GN would be a good base, but that older, and simpler engine flows better then a 3800, something to consider.

Ok, not really about size, but does a turbo have to be mounted level? Every one I've seen, whether it'* a diesel or a gas, the turbo has been mounted horizontal. I'm guessing that'* so it get'* oiled correctly? :?