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I agree with most of your explanation for manifold pressure but I'm pretty sure you have still made my point. (I think )If the pressure above the blade has no bearing then at our given 65 mph level road load, the blade angle will still be the same as NA or effectively fixed. The denser air will in fact go around the blade but it won't be carrying any more fuel than it would NA because a carb meters fuel based on air volume not air density and the mix will be slightly leaner. Kind of like the difference between 2500' DA and say -500' DA with it jetted for 2500'. Would you agree that if you could cruise steady state at a -500 DA while jetted for a higher DA that there would be the potential for a slight increase in fuel efficiency?


I come from a fuel injected world, where more air in equals more fuel in.
So, you're saying that this hypothetical engine's vacuum changes because it's getting more air, yet your explaination says," A carb meters fuel based on air volume.... My question is, where is the extra air in the engine coming from if a larger volume of air is not going through the carb? Do you think density has no bearing on a venturi? Do you think a carb's throttle angle is directly proportionate to fuel flow? Would you tune your carb to run richer than needed in one spot so you could make it run correct in another and expect a more fuel efficient engine? How about making it run clean everywhere? Your explaination seems to indicate it cant be done.




If density had a bearing on a venturi, you wouldn't have to jet a carb up for "good" air.

With all due respect an EFI setup has very little in common with a carb so to answer your question if I tuned a carb for max cruise fuel mileage it would be a given that it might not perform as well at WOT. That's the beauty of EFI, you can optimize for all loads or throttle positions. With a carb you can get it dead nuts for a VERY narrow range. Anything outside that at best will just be sorta close.

Kevin