mileage
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Senior User
Joined: Jun 1999
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mileage
Ok guys (and gals) I have a stumper for ya. I have a 77 F150 4x4 with a 351M in it. The engine is orginal with 120,000 miles on it. It has the stock 2bbl Motorcraft carb. I have the NP435 tranny and 29 inch tires.My problem is that I am getting terrible mileage (actually downright shi*ty) I am getting about 9-10 mpg. My friends have the exact same set up but his engine is new. I had some carb work done but the mileage is still not as good as it should be. I just read a post here that a guy built his 400 with HiPo stuff and he is getting 120 miles on a little more than 1/4 of a tank. I am getting 110 on more than a half of tank and my engine is bone stock. I do have tendancy to get lead foot syndrome but I have stayed away from that for the last 5 or 6 tanks of gas. So if anyone has an ideas on what is wrong please tell me!!!!!!!
Posting Guru
Joined: Jul 1999
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From: Inthepast
mileage
Mileage readings will vary by changes in atmospheric conditions, climate differences, how the truck is throttled, loaded, geared....you get the idea? It's almost impossible to compare one used vehicle to another, one driver to the another. If your "buddy" has the same set-up as you and you get poor mileage then there is something amiss. A tired or poorly tuned engine, driving habits all could factor into this. 9-10 isn't the worst I've ever seen, but a stock ride should get between 12-18. BTW--make sure you figure mileage after logging several fill-ups and a few hundred miles at least. I always found from some totally unscientific testing methods that my vehicles pulled better mileage readings when the tank was between 1/2 and full. [img]/dcforum/Images/happy.gif[/img]
<font color="#f80732" size="4" face="Graphite Light">Stock Man
</font><font color="#0000FF" size="2" face="Graphite Light">1967 F-250 FE 390 4wd</font>
<font color="#0000FF" size="2" face="Graphite Light">1966 F-250 I6 240 2wd LWB Flare Side</font>
<a href="http://www.hometown.aol.com/tbeeee">http://www.hometown.aol.com/tbeeee</a>
<font color="#f80732" size="4" face="Graphite Light">Stock Man
</font><font color="#0000FF" size="2" face="Graphite Light">1967 F-250 FE 390 4wd</font>
<font color="#0000FF" size="2" face="Graphite Light">1966 F-250 I6 240 2wd LWB Flare Side</font>
<a href="http://www.hometown.aol.com/tbeeee">http://www.hometown.aol.com/tbeeee</a>
Senior User
Joined: Jun 1999
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mileage
Your milage sounds fine to me. My parent's had a 79 F150 4x4, 351M, automatic, and they got 10mpg no matter what they did. Highway, city, towing, unloaded, my dad proved it to me one day. We drove up to Ashland (350mile drive) unloaded, got 10. Drove home loaded and towing a 24 ft boat, got 10 again. both tanks of gas both ways without stopping. (dual tanks). This was way before the new reformulated gas we got here.
I don't know what I get with my 78 F150, but with the engine about ready to crap out, I'm sure it's not even 10mpg.
I don't know what I get with my 78 F150, but with the engine about ready to crap out, I'm sure it's not even 10mpg.
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mileage
Hi, Fordman. I'm the guy with the built 400. My official mpg's are in now. I have 500 miles on old blue. I'm getting an average of 9.85 mpgs. I am also running 29 inch tire. I have 3.50 gears. Now that I have a few miles on it I am getting ready to switch to all mobil products. I highly recommend the 400 build I did. (it closely follows sept 98 hotrod) except I have 9 to 1 compression, 268 magnum cam, 600 carb. The motor has more power than my 98 5.4, without hitting the secondaries. I believe my milage will improve when I put 31 inch tires on her. With the 29" I'm turning 3000rpm at 75. My milage was calculated at this speed. 31" should bring my down to about 2600. Which should give me a couple mpg's. My engine has enough torque at this speed I don't thnk it will even know I am turning a larger tire. I'll let you know it the fluids help. The tires will have to wait till the 29" wear out. but that wont be long.
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Joined: Aug 1999
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mileage
I am no expert, but I do know this. I have a 400 motor. When it was bone stock I got 9 mpg. I even had a mechanic play with the carb to see if he could help it any. Made no difference. I changed to edelbrok intake and 4-barrel edelbrok carb and the mileage jumped to 12 mpg immediately.
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Laughing Gas
Joined: Nov 1999
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From: 15 miles west of Venus
mileage
FORDMAN,
YOU MAY FACTOR IN THE REAREND GEAR RATIO, TRANSMISSION(WHICH BY THE WAY HAS RECENTLY GIVEN ME A MPG OR TWO EXTRA) TIRE PRESSURE AND ALL THE OTHER SCIENTIFIC STUFF BUT WHAT IT PROBABLY BOILS DOWN TO IS AN OLD MOTOR (LESS EFFCIENT)I WOULD GET RID OF THE MOTORCRAFT CARB EVEN THOUGH I'M GETTING 15 MPG WITH ONE ON A 2WD F100 WITH A 400.
SCOT
YOU MAY FACTOR IN THE REAREND GEAR RATIO, TRANSMISSION(WHICH BY THE WAY HAS RECENTLY GIVEN ME A MPG OR TWO EXTRA) TIRE PRESSURE AND ALL THE OTHER SCIENTIFIC STUFF BUT WHAT IT PROBABLY BOILS DOWN TO IS AN OLD MOTOR (LESS EFFCIENT)I WOULD GET RID OF THE MOTORCRAFT CARB EVEN THOUGH I'M GETTING 15 MPG WITH ONE ON A 2WD F100 WITH A 400.
SCOT
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mileage
Hey I just switched over to mobil 1 5w 30. I drove the exact same route as I used on my 9.8 mpg trip. I tried to drive as close to the same speeds. It upped my mpg to 10.8 mpg. The mobil is going to save me $13 changing oil at 3000 miles. Changing to a synthetic may or may not help your loose motor. Mine has 700 miles on it now. It is still real tight. I also noticed my oil pressure gauge ,reads pressure the instant it fires off. Before it had a minute delay.
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Joined: Aug 1999
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mileage
I have a 77 F250 2wd and I haven't even attempted to figure out my mileage....
The reason is because my speedo is way off!! And if the speedo is off than the odometer is off too. When i'm going 35 mph on the speedo i'm flying by traffic. I think actual speed is around 55 mph.
My brother in law has a 79 F150 and a 79 F100 and both trucks had a incorrect reading on the speedo.
And my truck is all stock except for a new 351m in may of 84. The rear end, tires (16.5)and tranny (c6) are original equipment. Original snows on the *** end.
Same thing goes for my brother in laws truck
The f150 is a 302 with a 4spd
The f100 is a 302 with auto tranny
Is this a common thing on Fords to have inaccurate speedos?
The reason is because my speedo is way off!! And if the speedo is off than the odometer is off too. When i'm going 35 mph on the speedo i'm flying by traffic. I think actual speed is around 55 mph.
My brother in law has a 79 F150 and a 79 F100 and both trucks had a incorrect reading on the speedo.
And my truck is all stock except for a new 351m in may of 84. The rear end, tires (16.5)and tranny (c6) are original equipment. Original snows on the *** end.
Same thing goes for my brother in laws truck
The f150 is a 302 with a 4spd
The f100 is a 302 with auto tranny
Is this a common thing on Fords to have inaccurate speedos?
Thread Starter
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Senior User
Joined: Jun 1999
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mileage
I would have to say the ford speedos are not even close to being correct. The one in mine is off. When you set the speedometer at 70 and you count between mile markers it comes out to 40 seconds and that is 90 MPH!!!!!
Guest
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mileage
A relatively cheap and easy upgrade to improve mileage is to replace the timing chain &gears. Back in the early 70s ford retarded the cam timing on V8 engines to meet emmissions.This severley hurts mileage and power. If you replace the set DONT use the stock replacement,they are all machined with the timing retarded.Instead use a good double roller set with the 3 keyway crank gear and install it in the 4 position. You will probably have to adjust your distributor timing because the increased cylinder pressure will cause the engine to "ping" more but Im sure you will enjoy the increased power and mileage. Thanx
New User
Joined: Nov 1999
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mileage
Bill, have seen the gear sets, but haven't heard of setting up this way. Very willing to try this when I finish rebuilding my 400. It's in a '79 F-150 4X4. Just wondering if you knew of a reliable set. This will be my daily driver when I'm done with it. Because when finished I'm going to sell my '87 F-150 4X4. Will appreciate any info you pass on.Thanx.