If everything is maintained properly, freeing up the intake and exhaust should improve your gas mileage.
When I first started driving my car (I bought it used) my mileage went from about 18 mpg to 21 mpg.
Since then, my mileage has improved. I now get from20 mpg to almost 25 mpg.
My most significant engine mod has been an open element air filter (I'm using an SVT air filter base). Some other things that I did that may be playing a part in the gas mileage improvement are: 1) synthetic engine oil (Mobil 1); 2) synthetic ATF in the transmission; 3)replaced the original (awful!) Firestone tires with a set of Dunlop SP Sport 5000 tires in the same size; 4) I have some cool air running into the area around the air filter.
If I can get the cash together and justify the expense to my wife, a more open exhaust will surely improve my gas mileage (and horsepower) just a little bit more.
HTH
Mike
1996 SE MTX, Desert Violet (Ford's name for this color blows chunks! I prefer Black Cherry
)
Dunlop Sport 5000s, Ray McNairy's THFix,
Magnecor wires
