What mileage does your slant six powered ride get?

I have gotten high 20's maybe 30 mpg. But that was a built 170, .06 milled head with chambers within .2cc of each other, OEM 2 barrel carb and intake, MP cam, early 70's electronic ignition, and 2 1/4 exhaust and turbo muffler through the cast manifold. I think I was running 3.23 gears and an O/D manual transmission in a 64 Barracuda. Not 55 mph but definitely long highway cruise on level ground with a vacuum gage.

Best way to get mileage from a slant is adjust the valves, bump the timing up, and adjust the carb for proper AF mix. Get rid of the small exhaust. Use a vacuum gage and let off on the gas till it just keeps speed. The factory 2 barrel carb and manifold will give better mpg and power.