hey, i have a 93 945ti and ive done a few things to make it faster. the easiest stuff is opening up the intake and exhaust. there are a few things you can remove from the air intake system to open it up and add a k&n filter, a through tuneup/headgasket and check to the system for codes, magncor wires, hotter coil, bigger turbo, and 3' exhaust. ive done all of this and the car runs great and has alot more power. you can get a chip, install ford brown top injectors, get a better intercooler, change all the fluids to synthetic, ipd springs, sway bars, etc. there is alot of info and people modifying these cars. here are a few links to help you out.
http://forums.turbobricks.com/forumdisplay.php?f=13 all your performance answers
http://engstrom.net/ call for cheap jt 3" exhaust from sweden
http://www.fcpgroton.com/volvo.htm cheap replacement parts
http://www3.bc.sympatico.ca/Volvo_Books/archive.html free info on mods!
http://www.mcbrooms.com/volvo/fast700.htm alot of mod info.
http://www.sct-tuning.com/default2/900-turbo.php chips and more
http://www.volvonet.org/tpc/performance.html chips and more
and dont forget about the v8 conversion. its alot of money to get alot of power out of a b23 motor, this could be the same price. i did it to my 745 and it was a very fun, fast and reliable car.
http://www.converseengineering.com/