I guess the best upgrade you can try is an intercooler. The turbos we use are capable of more boost, and are often even set below spec. The idea being to get as much air into the engine (with proper fuel mix), an intercooler does two things. By cooling the air, it lets more air in for the same pressure, and it also cools the compressed air so that pre-detonation is less likely and not creating any timing problems. Many have added intercoolers to their 617 engines and claim a gain in hp, but few have any reliable dyno numbers to back up their claims. It seems simple enough that I have toyed with the idea of intercooling my cars, but decided that I have enough projects to worry about. There are many good candidates for intercoolers to be found on e-bay for low prices.
If you find that you can't get enough boost out of you current turbo (not likely) then you might want to consider a different one.
Garrett (airresaerch) T-3 is the most likely, though some had KKK units. It should say on the side of the turbo in huge letters.
Some of the ricers modify the turbos with T-3/T-4 hybrid turbos to mix and match for their desired performance levels. I really am NOT an authority in this area. If you want to find out more, I recommend magazines like "turbo" magazine.
Bear in mind that many problems exist with carelessly modifying the turbo systems, which could leave you shopping for a new engine. A Porsche 944 Turbo owner I know decided to crank up his turbo to 24 psi (usually absolute max pressure for a reliable daily driver motor is 14.7 psi), and he was lucky to escape with only a needing a new head gasket. Unfortunately, he was not a very good DIY and payed Fritz a couple grand.
Ive also heard that the boost on these is very modestly set, so wouldnt a little tweaking and rasing the boost a little help also? I am kind of on a tight budget so i think a new turbo is out of the question for now. Not sure an intercooler either.
Yes, tweaking the turbo is actually advisable. I read recently that this should be done on an annual basis (yeah, right!). Spec for your car may be at .8 or .9 bar (1bar=14.7psi), but many just go to 1 bar. Check the manual for specs.
To measure the boost, a "t" fitting is put inline between the injection pump "ALDA" and the intake manifold. A pressure gauge is then fitted onto the "t" with a line long enough to reach inside the car. The car is then driven to see the maximum pressure reached and the turbo is adjusted accordingly.
THAT part is not so easy, as the wastegate is integral to the turbo. I believe that procedure is also outlined in the online manual, but is different for the the make of turbo you have. Let me know if you can't find the procedure at http://skinnerbox.steaky.org/ , then i'll have to dig through my archives and e-mail it to you.
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