Best magnum MPG?

273 said
Cars weight and aerodynamics will be the ultimate limit to gas mileage and engines efficiency plays a big part but the engines we deal with have similar efficiency.

I really don't think weight has much of a role. Lots of heavy cars get pretty decent fuel mileage while it's easy for older cars/small trucks to get worse mileage while being significantly lighter among other reasons to not consider weight much.

Tantibus-74 said
Yes and no. 650 AVS is a very good carb. Easy to tune and great aftermarket support. I've tuned mine to get around 17 mpg. Which is pretty damn good considering the fact that I have 3.55 rear ratio, 3 speed automatic (non-lockup) and an airgap manifold.

You know something funny? I figured that was your gear ratio- I was looking around for your post you mentioned your gears because that was my max on a car with 3.55s.

I really don't like to touch anything related to a Carter carb. My experience with them hasn't been better- maybe I can't be bothered to tune them properly. Even though I got around 25mpg with my car tuned well, I could never be bothered to tune my truck's Holley better. It started adequately year-round including in the freezing weather and did great- fuel mileage wasn't horrendous but almost definitely could have improved. (like 9.8 loaded, 12.9 empty) I'm a big fan of simple- just set the choke appropriately according to the factory instructions and start it, then warm it up under way.