93 Supra Non Turbo
 

If I bought a 93 Supra and put a decent turbo on it, and run about 13 PSI, with full exhaust, and proper tune, how much HP would I be looking at?

You'd very likely blow the engine if you tried that on pump gas. The n/a engine isn't built to handle 13psi on pump gas, and neither is its ignition system. In other words, there's no way to "proper tune" high compression n/a pistons together 13psi on pump gas and the oem ecu. Even if you ran pure race fuel, the n/a ignition system isn't powerful enough to ignite under boost, so it would break up and not produce good power anyway. I'd suggest that you would be doing yourself a huge favor by starting with a full Mkiv TT if you want to make big horsepower (really!)...