Speaking of gas mileage, my 1940 Ford coupe made 250 HP with a much modified 289 and 3-speed 303 full-syncro tranny. With a 2100 two-barrel, on an aluminum double-plane intake, a 1" plenum spacer, electric fuel pump, mild hydraulic cam, cast iron factory headers for a GT, dual exhausts, hotter ignition, a bigger flywheel that was 10 pounds heavier, 2.79 rear gears, 29" tall rear radials and the car lowered for better drag-wind resistance, it got 25 mpg IF I KEPT MY FOOT OUT OF IT! Even with a big 2-barrel MPG goes south quickly when the loud pedal starts making noise! Reason for this build...with the 2-barrel there is less fuel to burn. With the plenum the fuel vaporizes better. With the mild cam, torque is made in the driving RPM range. With the heavier flywheel, "A mass in motion tends to stay in motion" comes into play. The 2.79 gears make for lower RPM at highway speeds, and with the taller tires, I just tapped the throttle about every 100 yards to keep it up to speed. A 40 coupe is very aerodynamic, and by keeping all under carriage parts tucked up close, air drag was minimized. The car weighed about 2900 pounds and was built for highway running. By building for that purpose I got the MPG I wanted with a nice Street Rod that was fun to drive.