Unless you want to turbo charge it with the parts from a 2.3 turbo out of a merkur or turbo coupe (or turbo stang if you can find one) you would have to modify the engine internally.
You could change the cam, put on underdrive pulleys and a low restriction cat back exhaust for a few HP. Also check out
www.superchips.com they should make a computer chip for your cars computer.