I have a 1980 F250 with a 1 ton dual rear wheel set up and a 351M that is getting old (118,000 mi). I am thinking of replacing it with a 400. Does the 400 use a lot more gas than the 351 and is it more durable? I need to tow a flatbed on a 4300 mile trip and I'm trying to explore my best options.

 

If you have a 351M, you basically have a 400 hidden underneath. I wouldn't spend the money on a second 400; you can rebuild the 351M into a 400 by replacing the crank and pistons.

The 400 isn't as bad on gas as some bowtie lovers will tell you it is. Look for another thread on here about what mileage different people get with their 400--a lot of it has to do with your application.

In my opinion, the 400 is incredibly reliable.

 

stkenn,

I looked into gas mileage before I built my engine up...most guys with mild buildups get around 13 consistently, with some as high as 14-15 if they keep their foot out of it. I keep my mileage in a logbook, and so far I am around 13.4 average. That includes occasionally hammering it while passing, and launches at stoplights around 10% of the time, with the Air conditioner running 90% of the time (I live in Georgia) - gas mileage is fine, but I like to enjoy my machine as well - and that has a mileage penalty I am willing to pay for.

- Grinning ear to ear with my 400.

DiMora

 

Any engine in a truck is gonna get "bad" mileage compared to a car. I get 17.5 MPG with my 400 equipped '71 Galaxie. The potential is there.

The "400 gets bad gas mileage" is a Chevy users rap, and is even repeated by some Ford drivers who should know better. After driving a 10 MPG 352 in a '62 Galaxie that only made 220 HP, I know some things about mileage.

The "400 is unreliable" is also a Chevy lie that I keep seeing repeated around this all Ford forum. My '71 400 has 230,000 miles on it. Unreliable, hell.

Funny thing is - my buddy's Chevy pickup sucks on gas mileage. He gets maybe 8. He's always yelling about it. Such experts they are. When I ran down and passed his supposed "race truck" in my '69 Galaxie at over 100 MPH with a bone stock 429 that gets 15.5 MPG, he was fit to be tied. He spent $2 grand on that motor and it was beaten by a stock Ford that gets twice the gas mileage.

He's rebuilt that 350 twice and I haven't rebuilt either of my Ford engines once. Talk about reliability.

 

I don't think a stock or mostly stock built 400 will get any worse mpg than your 351M. But you will notice more grunt from the 400.

 

For what it's worth.
I'm getting about 14mpg in town and 17mpg highway out of my 351m with
?38000 miles.
And I've towed every single Chevy my freinds have ever owned.
A fact they hate.
Steve

 

I only get 8 to 10 miles per gallon with my 400.

 

my 79 F100, C4, 2.75, stock 302 gets 9 city.
my buddy's 77 F250, 4sp, 3.31, stock 351M gets 16/19.

 

I think tires and tire pressure are a huge variable in this discussion, as being 1-2 PSI off can have a half gallon per mile impact or more due to increased rolling resistance. Also, an older engine that is in a poor state of tune can have a severe impact as well. My 400, with half the HP and 2/3 of the torque it now has with all my Edelbrock goodies, seriously got 6-10 MPG before I rebuilt it. (6 while towing, and ten on the freeway)...Bigfoot, with that kind of mileage, you must have monster tires, you drive with your foot "in it" a lot, or there might be some mechanical issues...Tell us more about your machine, would you? I am curious. I looked at your gallery...those look like some giant tires. Perhaps that is the big factor. Most guys will tell you that your 600 CFM Edelbrock will be plenty, even up to 500 HP or so.

 

dimora,
I have 33x12.5x16.5 super swamper tsl's on it and the tire pressure is always at 35 psi. That is whats on the side of the tire. When I bought the truck the guy told me he got 10 mpg no matter what he did. He drove 60 miles to work (back when gas was cheep) it got 10mpg. When he pulled his horse trailer it got 10mpg so I don't know. That was with the stock intake and 2bbl carb also. I have never checked it by miles but I only drive 2 miles to work and back a day and I use at least 5-6 gallons a week. I checked the gears and on the tag it says 373's. He told me he thought it had 409's but I figured it was 410's or 11's. At 55 mph the tach reads just over 2000rpm's. My 2000 ranger with 410's runs just over 2000rpm's at 55 also. So I really don't know why its that bad. Maybe I'm way off saying she only gets 8-10 but I think it is right.

 

With those tires, that sounds reasonalbe (8-10) just due to the rolling resistance. My gas mileage initially went up when I switched from a 2 BBL ro an edelbrock intake and 4 BBL carb...but that was only if I kept my foot out of it.

 

The guy I bought it from had regular truck tires on it not swampers and he got the same.

 

Believe it or not guys, with my 300 I-6, C-6 Tranny 2WD Bronco carbed at 8.000ft above sea level gets 8-10 MPG city in traffic! The I-6 is supposed to be, by the book, the most "economical" or should I say least of a gas guzzler among all Full-Size Bronco engines. Performance isn't great either, just average, and the engine is neither worn nor improperly tuned. So as you can see it's all relative. Actually I have driven the 351M and I liked it!, tons of power and torque; the 400 should have a bit more of those goodies... I've heard that the Ford big block engines are gas guzzlers, but our friend Scroob will tell us that such is a Chevy line... Of course I couldn't tell whether they are or not gas guzzlers other than pure logic: The bigger the displacement the fewer MPGs, all else being equal, for I've never owned one. If you can build the 400 to perform well and with reasonable, I mean around 12 MPGs then you should be in good shape. I wanted to put in a 400 (since it's real cheap!) instead of my 300, but I'd need to do something with the tranny, etc. My mechanic says "a stock 400 is a guzzler and unreliable" from what he's heard from other mechanics... Truth is that road and street conditions as well as the altitude factor have a greater impact here in Colombia on engine endurance and performance than in the U.S. of A. Ask Scroob, he is one of the top 400 experts in the forum! good luck in any case...

 

...Forgot... My tires are stock (P235-75R15) and I keep them well inflated even to the point that the ride gets too bumpy for rear passengers, but the benefits of such habit are many..., still het the 8+/- MPGs with the stock 1-bbl carb!

 

"a stock 400 is a guzzler and unreliable"? guzzler yes unreliable? Hell no it's still a ford man. I have had mine for 5 years leaks oil as fast as it burns gas (not really but sounds good lol) I have even ran it down to no oil showing on the dip stick lived 17 miles out in bfe and drove it to town to get oil and it never locked up. Mine is very reliable to say the least. As for the 300 not having power? I have and one and it was a hell of a runner in low lock I could go anywhere anyone else could. Just not as fast but I got there. The 460 (so I have been told) is better on gas then a 400 AS LONG as you stay out for the 4 bbl.