When gas was lowered the first time, in the Carter years, I pulled the 273 Commando with 72 340 heads since it had too much compression. I built a 170 /6 with the 4 speed and 2.76 gears. I could get 30 mpg on the highway. It was not stock. Mild Direct Connection cam, milled heads, cc'd chambers, 2 barrel carb and intake.