The 9C1s with the 5.7L have 260hp. I am not surprised it's a quicker car. The Caprice will run 0-60 in the 6s all day. You run a mid 7 stock if your car is an '88+. You have less than 225 hp and less displacement. Start by making sure the car is up to specs. Give the car a tune up, replace the fuel filter, change all the fluids, and dump Seafoam into the take and gas tank. Super expensive ignition systems won't do you much but lighten your wallet. A good quality cap, rotor, and set of ignition qires will do you jsut fine. Once you have the car running perfectly, then start tuning. Dropping the silencer, adding a K & N filter, and replacing the intake tube with one from a speed density Mustang are all the cheap go fast mods. A cold air intake won't add much but bling. The stock air intake minus the silencer is good for up to around 350 hp before it proves to be a restriction. Exhaust will help and I'd go with a catted X pipe with different length Super Turbo mufflers.
Gears will help, but I don't know how wild you want to go. If you get any gears, remember to get the proper speedometer gear to correct the instruments. Anything past 3.73s will not have a proper speedo gear. You might pick up a little performance and longer tranny life if you install a Baumann Engineering shift kit and A servo. A transmission cooler will help a lot for transmission life as well. If you drive fast on the highway, numerically higher gears bring up engine RPM and can affect gas mileage. If your limited slip differential is really worn out, you should look at getting it rebuilt or replaced.
When you want to spend the big bucks, then you need to look for new heads and a new intake. You can also look to add a supercharger. Basically, you're looking for mods for a 5.0L Mustang. You can start looking on corral.net for Mustang parts too.
In the end, I found it cheaper and easier to modify the car for handling. I decided to go that route first and ensure everything else was up to snuff and then add power later.
Have any pics of the car?
