Dinan chip, BAS plug wires, SuperSprint exhaust, K&N cone filter w/a heat shield, a 4.27 l/s from a 318iC, octane booster, some good rubber, and a tune-up should do the trick. My '91 318i was an e30 325i-catcher with these simple mods. Cost roughly $1250. Or, all that plus a Downing/Atlanta supercharger (change belt drive over to serpentine and modify a few brackets) and a 4.45 l/s from BAS. That made my '92 318iC an e36 325is-catcher (and maybe a 300,000 mile M3-catcher!)!! Costs roughly $5000 for that M42 mod, but money well spent.