390 FE mpg
Logistics Pro
Joined: Feb 2011
Posts: 3,522
Likes: 11
From: Townsend, MT
So I've heard rumors that the 390 in the old thunderbirds get around 15-17 on the highway...I have a 390 out of a cougar i and its all rebuilt,pretty much stock except for the bolt ons,headers,intake,and truck avenger carb....oh and a mild rv cam and adjustable rocker arms....I'm running the stock gears out of a 79 bronco with 35" toyo M/T tires, and I have a 4" lift,what should my MPG be with these specs? I can't drive it yet because it's goin through the last stages of resto...
More Turbo
Joined: Oct 2011
Posts: 636
Likes: 5
From: down a red dirt road
well my 2wd got 17 with a wore out 360, until blowby was uncontrollable cuz the rings were no more and it quickly dropped to 9mpg's. its a camper special with 3.73's (dana 60) stock with performer intake and headers, electric fan and msd.
i just got done with a new 390 so i hope its the same or better?!? once broke in i want to go synthetic but need a great ZDDP additive before ill trust it.
last year randy's ring and pinion still had a set of 3.07 for the dana 60, it required a different size carrier than what mine has tho. they made two sizes.
i would switch out to a 9 inch but i love having 8 LUG and the fact that a dana 60 is close to bulletproof. im going with bigger tire sizes to makeup for the gear ratio instead. my goal is getting my 70 mph RPM a lot lower than 3000+. i think im gonna have to break down and get an overdrive.
i just got done with a new 390 so i hope its the same or better?!? once broke in i want to go synthetic but need a great ZDDP additive before ill trust it.
last year randy's ring and pinion still had a set of 3.07 for the dana 60, it required a different size carrier than what mine has tho. they made two sizes.
i would switch out to a 9 inch but i love having 8 LUG and the fact that a dana 60 is close to bulletproof. im going with bigger tire sizes to makeup for the gear ratio instead. my goal is getting my 70 mph RPM a lot lower than 3000+. i think im gonna have to break down and get an overdrive.
Post Fiend
Joined: May 2012
Posts: 14,724
Likes: 0
From: Gods Country, Kansas
It could also make a difference between 4-speed vs 5-speed and between auto vs manual.
The manual will get better mileage and the 5 speed will get better than the 4-speed because if you are in 4th with high RPMs going 65 you can shift to 5th and be going 70 with low RPMs.
The manual will get better mileage and the 5 speed will get better than the 4-speed because if you are in 4th with high RPMs going 65 you can shift to 5th and be going 70 with low RPMs.
Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 82
From: NorCal
well my 2wd got 17 with a wore out 360, until blowby was uncontrollable cuz the rings were no more and it quickly dropped to 9mpg's. its a camper special with 3.73's (dana 60) stock with performer intake and headers, electric fan and msd.
i just got done with a new 390 so i hope its the same or better?!? once broke in i want to go synthetic but need a great ZDDP additive before ill trust it.
i just got done with a new 390 so i hope its the same or better?!? once broke in i want to go synthetic but need a great ZDDP additive before ill trust it.
However for comparison, my brother's 2WD 69 F100 (360/C6/3.00) got 15.7 mpg at 65 mph from SF to San Diego. That's darn good for an FE. And I used to have a 2WD 76 F150 (302/C4/3.00) and it regularly got 17 mpg with a light foot. Towing anything were horrible experiences.
More Turbo
Joined: Oct 2011
Posts: 636
Likes: 5
From: down a red dirt road
right hio,
we all know the 4x4 is gonna be less mileage, its heavier. i just wanted to throw some optimism in here for FE's, and yeah towing is another story too
we all know the 4x4 is gonna be less mileage, its heavier. i just wanted to throw some optimism in here for FE's, and yeah towing is another story too
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Post Fiend
Joined: Apr 2008
Posts: 8,261
Likes: 15
From: Big Sky Country
My '75 highboy with a mildly built 390, 4spd, 4.10's and 35's only gets 8mpg, that's all in town, stop-n-go, 25-55mph... but i drive it very aggressively, all the time, it's too fun of a truck to drive any other way, so i drive it like i stole it.
Personal driving style goes a long way in the mpg department, i experimented once with a full tank of gas to see what kind of numbers i could get, i drove around like an 87 year old retired librarian who plays the organ at her church every Sunday, i got roughly 10.5mpg from that tank of gas, but what fun is in that.
Lead Driver
Joined: Mar 2008
Posts: 7,182
Likes: 380
From: Near Los Angeles
I have a 75 f250. I ran it with 3.74 gear with a 360, 2v, and got 10 mpg, rain or shine ... on the freeway, with oem tires/rims. I changed to 3.31 gears for about $500, and got 10 mpg on the freeway. I changed to a 390 and got ... yep, you guessed it, 10 mpg on the freeway.
Then I saw the light: I beefed up a 300 inline six to the same hp as the 390 with a 2v carb, etc. With the 300 I get over 15, 16 or 17 mpg on the freeway. With the addition of a ZF trans, I should get close to 20 mpg on the freeway.
Then I saw the light: I beefed up a 300 inline six to the same hp as the 390 with a 2v carb, etc. With the 300 I get over 15, 16 or 17 mpg on the freeway. With the addition of a ZF trans, I should get close to 20 mpg on the freeway.
Thread Starter
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Senior User
Joined: Sep 2012
Posts: 141
Likes: 0
I have a 75 f250. I ran it with 3.74 gear with a 360, 2v, and got 10 mpg, rain or shine ... on the freeway, with oem tires/rims. I changed to 3.31 gears for about $500, and got 10 mpg on the freeway. I changed to a 390 and got ... yep, you guessed it, 10 mpg on the freeway.
Then I saw the light: I beefed up a 300 inline six to the same hp as the 390 with a 2v carb, etc. With the 300 I get over 15, 16 or 17 mpg on the freeway. With the addition of a ZF trans, I should get close to 20 mpg on the freeway.
Then I saw the light: I beefed up a 300 inline six to the same hp as the 390 with a 2v carb, etc. With the 300 I get over 15, 16 or 17 mpg on the freeway. With the addition of a ZF trans, I should get close to 20 mpg on the freeway.
but I know the 10 mpg thing as well my grandpa had a 1990 dually with a 460 and wether you were haulin *** or driving like grandma you got 10 mpg....that was a 5 speed though. And it was EFI