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That was an economical set-up in 1974 . . . but standards have changed. And that was in the days of low compression ratios as car-makers were figuring-out emission controls.

Would help to know what transmission & rear axle you have..........can tell you that we recently had a cherry, low-mileage Camaro (same chassis as Nova - probably a little heavier) of that vintage: 350 4 barrel, hydro 400, rear axle something like 3.23. If driven carefully we got 14 mpg avg........9 around town.......16 highway. You'll do better than that, but not much.