Engine Performance

Headers, FF muffler, CAI, advancing the timing, computer mods like Ultra power will all increase performance but unlikely to increase MPG. Headers, FF muffler, CAI, advancing the timing increased my performance as measured from 40-60 mph. As others have said wires, plugs, and general tuneups help also. My baseline performance when I first bought the MH was 22 secs. After tuneup it dropped to 19 secs. Headers, FF muffler, CAI, advancing the timing further reduced the time to 12 secs and added about 80 hp. An 8.1 engine is more efficient the the older 454 so you will likely get about half the increase of HP and performance with these mods. The only increase of MPG that I saw was adding a vacuum gauge. By trying to keep the gauge above 10 ins of mg, I saw an increase of MPG from 8.5 to 8.7. Good luck in what ever you decide to do.