which engine can get the best fuel mileage?

My wife was in a wreck and her car has been totaled. (she is ok besides broken ribs) This means that I will have to start driving one of my trucks as a daily driver. No doubt it will be the 1984 F150 and not the project truck.

The engine in the 1984 is a 300 inline six. I have converted it to duraspark ignition and a non feedback carburetor. It has issues that have to be addressed and will need a fresh-up.

Can the 300 inline six be built to get better fuel mileage? (I currently get 14mpg)

The other option I have is a 351. (It will have to be rebuilt as it has 425,000 miles.) It will bolt directly behind my current transmission as the two engines share the same bell housing pattern. Can it be built to get better fuel mileage than the 300 inline six?

Might consider the in between...302 EFI

FalconEh wrote:Might consider the in between...302 EFI

X2

351w put a carb and intake on it with a rv cam yes the trans with work but you will have to change the flywheel to a 351 flywheel my 351w in my 69 gets around 16 mpg as long as I stay out of the 4 barrel it has a c6 with 3.25 gears

FalconEh wrote:Might consider the in between...302 EFI

I only have a 351 and the 300 laying around.

supervel45 wrote:I  would stick with the 6cyl.. It will run about like the 302 and they will all get pretty close to the same mileage and won't be worth the trouble of the swap.

I agree that I would rather fresh'n up the 300 six cylinder over doing another engine swap. For towing my other truck on a trailer would the 300 be able to pull the load adequately? Right now the 300 won't pull my 1200lb Polaris sxs ranger and maintain hwy speed going up slight hills. (The ranger sxs does have a lot of frontal area that causes a lot of wind resistance as it pulls much better at 50mph than 70mph.) Keep in mind that it has 3.05 gears and 31" tall tires, I don't know how much the proper gearing would help.