I own a 1990 Iroc with the 305 TPI and 5 speed and it is mostly stock other than home made ramair, airfoil, and msd coil. I really cannot afford expensive mods and was wondering what i could expect from an adjustable fuel pressure regulator and injectors. Also what psi should i use and pound of injector should I use without having to change my computer.Or any other mod that is a good bang for my buck.

You will not notice a difference with bigger injectors on a basically stock car and an AFPR is more of a tuning tool. Best bang for $$ is exhaust or headers

best thing would be to do a whole tuneup first, you've already started by changing your coil but dont' overlook plugs, wires, oil, air filters, and things like those, start from there and then go on to bigger upgrades such as exhaust or headers

i agree a full tune up would be in order, then go right to exhaust..

port your plenum