Studying the fuel economy difference between the
1992 Ram Magnum 5.2 V8 and the
1994 Ram Magnum V10
is a valuable way to build knowledge.

How does engine size, gearing, aerodynamics and weight affect pickup truck fuel economy?

An (almost) silly question:

On a level blacktop highway how much of a pure tailwind speed does a
1971 4wd Ram with a 440 V8, manual trans and 3.92 diff
have to have blowing to match the zero windspeed MPG of a
1994 4wd Ram with a Magnum 5.2 V8 46RH and 3.21 diff ?

The Windows computer program “Fuel Economy Calculator”
from Performance Trends Company
is the only under $200 program I know of
that can give a plus or minus 7% answer
to that question.

The V10 had some horrific real world MPG numbers if I recall.

My 2WD V10 dually with 4.10 gears got 9 MPG pretty much no matter what except with the 30' enclosed trailer behind it, then it got 6.

You recalled correctly. I decided to with the 5.9 when i was in the market for a second gen. The V10 didn't offer MDS that's why it used so much fuel(it's 488 cubes!).

I have a stock 1974 D100 440 with 3.23 gears and 29 in tall tires and I routinely get 11-12 MPG unloaded and around 9 mpg pulling a load, with either a Thermoquad carb or a Edelbrock 800 AVS style carb, if I put an overdive behind it it would probably get around 15-16mpg.

Getting 6 mpg out of your setup is way too low, holley carbs are great peformance carbs but sometimes take a little work to get fuel mileage out of them, they are generally setup fairly rich out of the box. I had a Thermquad carb on a 440 in my 69 Charger and it would routinely get 15mpg and when I dropped an out of the box 750 vac secondary holley on it the mileage dropped to 12mpg but the throttle response and power was noticably improved.

Another area is to check and make sure your ignition timing is set right, you should be in the range of around 10-12 degrees initial timing and 36-38 degrees total timing all in by 3000 rpm (assuming you don't run into detonation problems) and make sure the vacuum advance it working, with the vacuum advance working the timing should be in the 52-56 degree range. All this can have a significant effect on fuel mileage and power.

It seems your dead set on a 318 engine but this info might help if you decide otherwise.

Kevin