Increase Fuel Mileage
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Freshman User
Joined: Jul 2005
Posts: 28
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From: Southeast TN
Increase Fuel Mileage
I am about to rebuild my 78 F150s engine and I was wanting to get the best mileage I could out of it. I was getting about 12-13 mpg out of the 351M with 2.75 gears. While I am getting new engine parts, what upgrades could I get to increase the mileage? Should I go with a new cam, rockers, or what else? I also need the part # so I will know what to look for.
Posting Guru
Joined: Mar 2002
Posts: 2,070
Likes: 2
From: Boise, Idaho
I would use a stock cam and degree it straight up. I think the stock tune on the carburetors were set to the rich side to reduce NOx production (and help keep the catalytic converter hot). Rejet the carb. If you're really serious about mileage, make sure the EGR systems is in place and working. The rich tune of the stock carb tended to gum up the EGR valves, so leaning the carb will help keep the EGR working. If you're not a believer in EGR, then make sure the advance of the distributor is tuned for a non-EGR engine.
There aren't many iron 4bb intakes for a 351M. I've seen where someone modified his iron 2bbl to make it a 4bbl. I don't know how hard it would be to get an iron intake welded to fit a 4bbl. It could cost $200-300.
There aren't many iron 4bb intakes for a 351M. I've seen where someone modified his iron 2bbl to make it a 4bbl. I don't know how hard it would be to get an iron intake welded to fit a 4bbl. It could cost $200-300.
Elder User
Joined: Jan 2005
Posts: 797
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I've got a 400 stroked .030 with some other goodies, I get 10mpg unloaded regardless of how I drive, hook up my travel trailer and I get 5mpg regardless of how I drive. Had the carb worked on and set up by a local garage with a good rep for carb work, and now I get 10mpg unloaded and 5mpg towing. I find the only way to get good gas mileage from the truck is not to run it at all. As for parts and advice so far the other posters are right on.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
Raising the CR will help some($$). Also running the cam straight up should help(cheap).
A good Sequential EFI setup shoulld also help($$$).
A good Sequential EFI setup shoulld also help($$$).
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I'll have the Roast Duck
Joined: Jul 2002
Posts: 9,622
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From: Northshore, MN
FWIW, in an emergency, I put my 74 F100's 302 2v carb on my 78 Bronco's 351M intake. What it did was shock me....I got a bit better mpg, and better throttle response. My 2 cents.
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Posting Guru
Joined: Dec 2002
Posts: 2,003
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From: chicago burbs
Bouts21, i was just curious what you have going on in there...
for a serious gas mileage build i'd do the 400 upgrade if the budget allows, with a Comp Cams 240H or 252H but watch the dynamic compression with these small cams if you plan on using TMI pistons. either a fresh stock carb and stock intake or an S.P.2.P. manifold with a Holley Economaster carb on it, and 2 > 1 single exhaust with a low restriction turbo muffler.
for a serious gas mileage build i'd do the 400 upgrade if the budget allows, with a Comp Cams 240H or 252H but watch the dynamic compression with these small cams if you plan on using TMI pistons. either a fresh stock carb and stock intake or an S.P.2.P. manifold with a Holley Economaster carb on it, and 2 > 1 single exhaust with a low restriction turbo muffler.
Fleet Owner
Joined: Sep 2005
Posts: 28,609
Likes: 18
From: Lake Tahoe, Nevada
Here's an old, long, gas milage thread.
https://www.ford-trucks.com/forums/4...mpg.html?pp=15
plenty of bs but some really good stuff too.
https://www.ford-trucks.com/forums/4...mpg.html?pp=15
plenty of bs but some really good stuff too.
Posting Guru
Joined: Mar 2005
Posts: 2,068
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From: western montana
i'll be building anoher 400 for a combo of mileage and power in my daughters (16 in aug) 70.5 falcon (torino body). It will have the typical 268-272 or so duration build with good compression etc. I also plan on putting a gear vendors over/underdrive and 3.25 or so gears so the final drive will get her 2500 rpm at 80mph. I am expecting that she will get over 20 hwy and still be able to kick some hiney at the 1/4 track. Hoping to get 380hp and 450ft lbs.
planning the build now...just got the weiand intake. From my research the 400 can make good power in an economic way. Gearing and weight is huge. Gotta say I'm still considering going with the alloy heads and getting her up over 400 ponies...well see.
planning the build now...just got the weiand intake. From my research the 400 can make good power in an economic way. Gearing and weight is huge. Gotta say I'm still considering going with the alloy heads and getting her up over 400 ponies...well see.
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