xfi had a FE cam , 2 ring piston , and CPU for better mileage . it got about 50 mpg from the factory. i've done the same with a lsi car . it has an advanced cam gear , mileage cam , power pulley ,2 inch open exhaust , 13/175r13 tires (50psi) and high speed transmission. i get 50 mpg average with this combo, even with the heaver car body.
check this link for more
http://www.teamswift.net/search.php?...&submit=Search