When I went from 2 1bbl Rochesters to 2 1bbl Carters on a '58 235 with Fenton headers, Mallory ignition and dual exhausts my gas mileage went from @11MPG to 15 MPG around town and about 17 MPG on the highway. I also installed a fuel pressure regulator to bring the fuel pressure down to about 4 1/2 to 5 lbs.
