I dont know much about the new carbs like demons,I have mostly had carter AFB's and the edlebrock clones they now make--if you want the best mileage,smaller CFM carbs are available,like the 390 CFM Holley carb,and edlebrock and carter make a 500 CFM version of their 4 barrel carbs--and the smaller size barrels keep the velocity of the fuel moving more quickly,improves low end tourque,and avoids bogging.But if you have a big cam,higher than stock compression,and headers,you may have to use a bigger jetting,or even a bigger carb to avoid it running too lean,lean is good for mileage but you cant let it go too lean or valves can burn and pistons can melt.I ran a 450 CFM on a 74 454 years ago,one of those "Economaster"carbs--I had nothing else hanging around the shop,so I threw it on just to get me to work till I could buy a better carb--but I was suprised how much better it ran than it did with a 600 Holley that was on fire most of its life--I got 15mpg with it,and the 4 barrel would put you back in the seat.Everyone said I'd burn the valves,but I ran it back and forth to NH and VT many times,no real problems,it would ping in the mountains if you ran regular,but nothing premium gas didnt quiet.I think a lot of engines are over-carburated,even from the factory(at least the CFM of the 4 barells)Sometimes LESS is more! /forums/images/graemlins/crazy.gif
