You may like to read up a bit here about BSFC:
https://help.summitracing.com/app/an...hat-is-bsfc%3F
BSFC = lbs. of fuel used per hour ÷ horsepower
For example, a 300hp engine using 150 lbs./hr. of fuel would have a BSFC of 0.5.
Your average Cobra needs less than 30 hp to cruise at 65 mph. You need to place your most efficient rpm at that speed.
And the A/F ratio needs to be right at that rpm, too. If you had a Holley carb you would want to jet the primaries accordingly and make sure your power valve is closed.
Your cam with .600 lift should have quite a bit of overlap where fuel consumption is higher at lower rpm. It's throws out unburnt mixture. (That cam's most efficient rpm is higher than that of a mild cam). Higher rpm however comes with more friction.
What I am saying it, if your highway speed rpm is too low for the cam, you might use less fuel in a higher gear!
My car's rpm was 2.500 at 65 mph and it would have benefitted from 2.000 rpm at 65 mph (i.e. a 5th gear). But perhaps not 1.500 rpm when the cam was still off.
What messes with fuel consumption of our V8s is a radical (low vacuum) cam where the power valve is not matched to keep the power circuit closed. This should only open at WOT (when vacuum is, again, low)
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