Gas mileage 225 Slant 6

I daily drive my 73 Dart (Known as the Shart because Stretch has a Dart :D).

I live in a very rural area of upper Michigan so my daily commute is a combination of back roads and 2 lane highways with 55 M.P.H. being the max speed. Its about 25 miles to work with two small towns to slow down through. I average 21 M.P.G. back and forth to work and on a recent road trip (200 miles round trip on two lane highways) I averaged 29 M.P.G..

My car is a 225/904 with unknown gears, 4 wheel manual drums and 14 x 5.5" wheels. I rebuilt the carb, adjusted the valve lash, did a basic tune up, replaced all the vacuum lines and replaced the intake/exhaust gasket. I set the base timing at 12 deg. BTDC. I custom bent a 2 1/4" dual exhaust system with two cheap reverse flow "turbo" style mufflers. I made a new down pipe and installed a "Y" to split to the duels. I also set the wheel alignment at .5 deg. negative camber (both sides), as close to 3.0 deg. positive caster as I could get while keeping the camber at .5 negative, and set the toe at 1/8" in.
I have collected the parts required to convert it to a A833OD this winter. I just need to rebuild the transmission and find a flywheel. It will be interesting to see what the OD does to the fuel mileage.