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Aug 7, 2000 | 11:35 PM

jamesclizer

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I have a '76,f-150, 390, C-6 4x4.I run a3:50 gears, 9" rear, D-44 frnt. Also 33x12.15 on 15x10 rims. My engine runs faster than it's moving on the hi-way,say65-70 mph. It does great offroad,Iwant to either put a manual overdrive on the c-6, or change my diffs.I want to keep my tires as they are. My gas mileage is horrible on the hiway.Which way would you go, overdrive or gear change??

Aug 8, 2000 | 07:09 AM

jowilker

Fleet Owner

Joined: Jun 1999

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From: Creedmoor, North Carolina

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James, It seems that there is a ton and a half of you guys that think the 4X4 is so kool and you have to have one, and that's fine by me. You are in love with it's off road abilities, makes for a great testosterone rush, real manly. Climbing over things, running through three foot deep mud holes, but then when it comes to what you do with it 98% of the time, you want it to get Escort gas milage. It aint gonna happen, sorry. The truck was not designed to get gas milage. You can get aftermarket overdrives but they'll cost darn near what the truck is worth.

Save and buy a daily driver of some kind so you can keep your toy.

John
jowilker@nc.freei.net

66 F100s
In the still cool hours of the night, you can hear chevys rusting away.

Aug 8, 2000 | 09:13 AM

dave186

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Youve already got high gears, and big tires so I dont think the gears would help. What do you call horible gas mileage? My truck is the same as yours, but it has 32" tires and 4.10 gears and gets 11-12 mpg sometimes 13 if I be nice to it.
Dave

http://www.davesmonsterpit.com

Aug 8, 2000 | 09:17 AM

dave186

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Forgot to mention I have an NP-435 4 speed.
Dave

http://www.davesmonsterpit.com

Aug 8, 2000 | 01:05 PM

hillbillyk

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Joined: Jul 2000

Posts: 851

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From: Elkton, MD

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Nothing will help these old 4x4s with gas mileage, I have a 79 bronco, c6 auto, 3.50:1 gears, 400m, I can drive it easy or hard, the best I can do is 10mpg, it did the same with the original 351m. I think the gas mileage is worse on the highway going 65 or 70 then when running 55. My 74 f250 4x4 gets much less than 10 with a cg, 390fe, and 4.10:1 gears. I used to have an 84 f150 4x4, c6auto, 3.55:1gears, with the original 302 I got 10 mpg, then built a 351wHO and still got 10, no matter how hard I drove it, these old trucks just like gas, but at least they have cheap insurance and no payments, and no computers to go bad. my 2 cents

May 21, 2001 | 07:30 PM

gsxrsquid

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the 390 is not noted for economy. You might try putting in an ecomy/torque cam from someone like ISKY and adjust jetting on carb to lean it out a bit. The manual overdrive can't hurt. Good luck

May 24, 2001 | 10:53 PM

dinosaurfan

Cargo Master

Joined: Aug 2000

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From: SW Michigan

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James, just what kind of mileage are you getting right now anyway ? What condition is your engine in ? I ask because most of the 390s in trucks came with a very low compression piston, if you were near rebuilding time you could use flattop O deck pistons and the engine will give better mileage. Just a thought. DF