Hey all, I just installed a fresh 400 rebuild in my truck, same motorcraft 2v carb and manifold, stock rebuild except for timing chain and cam. My mpg right now is around5-6 intown, I know motors are tight when they are fresh but this seems really low. Before the rebuild I could count on around ten in town and 14 Hwy, maybe I will gain 1-3 mpg's after breakin. But this is worrying me.

What are you people getting for mpg with your 400's?

 

Here this should make you feel better .

In My Pull Truck I run Low Range 2nd Gear during a pull.Most pulls are 300 feet long. I usally end up in the 285 to 295 foot range.
I burn 3 Gals of Phillups B 33 racing fuel at $9.50 a Gal. per pull, And I pull in two classes at each event .
So every two runs it cost me about $57.00 .... How far can you go for $57.00 in your Truck.

 

Well I have a '78 currently with a 351M c6 tranny, 33" tires, 3.50:1 rear end and around town I get about 8-9mpg. Its a stock rebuild except I added edelbrock aluminum intake, holley truck avenger carb (670cfm), free flowing dual 2.5" exhaust with dynomax headers. But I am still tunning in my carb and timming. Its been an ongoing tunning adventure lol!

 

Thanks for the info, guys. I know I will at least get 8 mpg after a thousand or so miles, I just felt that what I was getting seems really low.

 

I would make sure you don't have any restrictions in the intake or exhast. Also use as much initial timing as you can. It will pick up the power band on the bottom end.