I put a new 351 M in my truck a couple years ago and have a couple thousand miles on it since. I expect to be driving it more in the future and would like to hear any tips on improving MPG.

Back when I drove it regularly, I put a high rise intake manifold and 4 BBL, 600 CFM, carb on it and my mileage improved drastically (30%). Since I haven't driven it much, with the new motor, I don't know what to expect.

Any suggestions?

 

It depends greatly on auto trans vs manual, ring/pinion gearing, 2wd vs 4wd, tire size and cruising speed.

I run a bone stock but healthy 351 in my 77 F250 with a 4 spd trans, 4.10 gears, 4wd and 35" tires.

I have to add about 11% for actual speed and actual miles traveled due to my tires.

I run at 55 mph on my speedo which is actually closer to 61mph on GPS.

When the weather is nice I can pull 12 mpg. Lately we have been stuck in a -20 degree to -30 degree cold snap and I figured this morning as I filled the tank that I only pulled about 9 mpg during that terrible cold. I also did some 4 wheel drive running in deep snow to cut and haul a load of firewood on that tank.

The mpg stuff is really pretty simple.

It's cubic displacement, and speed at RPM

If you can achieve a reasonable cruise speed while keeping the RPMs down you'll be doing about the best you can.

I do like the 351 engine over the 400 in this respect. I know the 351M don't get much love But I have a few of them and I like em.

We also have a 79 F150 with the 351M, 4 spd trans and 3.5 gears.

It's parked right now and slated for project/build very soon. The sooner the better I'm thinking, lol!

I expect to pull 14 mpg with the truck I just mentioned with 33x10.5 tires.

 

I have a 3 speed auto trans, don't know the gears, and it's a heavy truck. It was a camper special with dual everything (batteries, exhaust, gas tanks, etc.) and heavy duty suspension. Prior to the manifold and 4 BBL I got 10 and after, I got 13, so it paid for itself.

Just don't know if there are other things I can do to help.