Hi, Dan
Turbo identification, quick method:
Earliest cars, Garrett T3: CHRA (Center Housing Rotating Assembly, as it's known) is bolted to the turbine housing with 6 bolts and two semicircular plates. The compressor housing has AIResearch embossed on it. In the 740/760 it uses an external CBV (valve bolted to the head that has a rougly 1" ID hose from the compressor discharge hose and returns to the compressor inlet hose.) Exhaust manifold has "flat" runners, and the turbo bolts to the manifold from behind the manifold (turbine housing is threaded). Very few were not water cooled, but some were. Here's a picture of the Pierburg CBV:
'88-'89, Mitsubishi TD05: CHRA is fastened to the turbine housing with a V-band clamp, compressor housing has an integral CBV. This turbo was only ever used with the flat early manifold as well, so the turbine housing is threaded and bolts to the manifold from behind the manifold.
'90+, Mitsubishi TD04: CHRA is fastened to the turbine housing with a V-band clamp again, but this time it's bolted to the manifold from the front, so you can easily see the nuts holding things together. It's also going to be on the more desirable "90+" manifold, more desirable that is if it's been opened up and hasn't cracked. The manifold has round runners, no flat sides. The turbo also has an integral CBV, but there are two styles - straight and angled. Angled is later.
Random, Garrett T25: CHRA is bolted to the turbine housing like the Garrett T3. It distinguishes itself from the earlier T3 by an integral CBV like the Mitsubishi. I think it came on both early and late manifolds.
In looking for images, I found this site:
http://www.nuceng.ca/workspace/Volvo%20 ... cation.htmIdentify your turbo first, and then we should discuss options. You might even want to upgrade, and not bother with the same turbo. If you change turbo families, though, you will probably have to problem solve some minor plumbing issues.