Gas Mileage
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Senior User
Joined: Apr 2003
Posts: 330
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Gas Mileage
I am working on a 79 F-160 4x4 w/ 351m and T-18. I have heard a lot about making the 351 into a 408 using a 400 crank, pistons, etc and boring it out. I havent really heard anything about the gas mileage for the 408. Was just wondering cuz i do not have enough money to have a daily driver plus a toy or get 9 miles to a gallon out of my daily driver. And also is this worth the money? I have been told it is one of the best ways to get the most power out of this engine. And i do love the engine now all i have done is bigger cam n different pistons so far. Would like feedback from anyone currenty running the 408 or anyone who knows about it.
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Senior User
Joined: Apr 2003
Posts: 330
Likes: 0
Gas Mileage
well i do not know for sure. i was talking with the mechanic who lives by me and is helping me with this project and we were deciding between a few options. They have had to order a rebuild kit for the engine due to the fact that the bearings were bad and it messed up crank etc. one of those chain reaction deals 
Lead Driver
Joined: Nov 2000
Posts: 6,646
Likes: 352
From: Albuquerque
Gas Mileage
The 408 is just a 400 with .030 overbore. It's a good engine but with a 4x4 I wouldn't expect more than 10mpg. If you check out peoples signature you will find a lot of info on what guys have done.
Fleet Mechanic
Joined: Jan 2003
Posts: 1,812
Likes: 15
From: Central Ohio
Gas Mileage
My 351M in my 78 bronc got as low as 7mpg with the stock carb and a holley truck avenger that I could get tuned right. I have gotten as high as about 9.5 mpg with an edelbrock 750. Still using stock short block, cam and heads for now. Using reasonable gearing of 3.50:1 with 33" tires and a c6 tranny.
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New User
Joined: May 2003
Posts: 10
Likes: 0
From: NW Indiana
Gas Mileage
You arent doing anythign special there. Just creating a 400 that has been bored. Gas milage will be appropriate for a bored out 400. It isnt like you created an engine like a 383 Chevy. 400's burn gas, thats a fact. Build the 351 and have fun.
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Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
Gas Mileage
Your mileage primarily depends on your gears or final drive ratio, camshaft, and to a lesser extent your carb and exhaust system. In order to get optimum results all of the system components must be carefully matched.
Elder User
Joined: Dec 2002
Posts: 925
Likes: 0
From: Quaker Hill ,CT U.S.A.
Gas Mileage
Check out this post :https://www.ford-trucks.com/forums/s...hreadid=116129
Basically drive the speed limit and take off easy and you wont be feeding the beast as much !
Basically drive the speed limit and take off easy and you wont be feeding the beast as much !
Junior User
Joined: Nov 2001
Posts: 57
Likes: 0
From: Renton USA
Gas Mileage
Have a '79 F-350 Supercab 4x4 with a 4 speed manual tran. and 3.54 in the axles with the 400 that back when the engine was healthy (prior to 3 burn valves and one 0 compression cylinder and 265,000 mi. on it) I got between 12 to 14 mpg, towing = 889 mpg and racing = 6 mpg.The engine had a 625 cfm 4v carb, r/v cam, Edelbroch "Streetmaster" intake manifold"(pre Performer) I have a straight up timing chain and gears,] and dual exhaust (no headers) retuned distributer. Prior to the mods I got around 9-10 mpg. Mike B.
