fuel mileage with 390??

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fuel mileage with 390??

Postby gregamorton on Mon Feb 28, 2011 8:07 pm

Guys just curious what fuel mileage you are getting with your 390 trucks? Mine is a 1971 crewcab 4 speed with 4.10s. I am looking for a 3.54 rearend as I dont need the low gears but here is what its getting.

1st tank ran half out and it got 8.2mpg

2nd tank ran it half out again but this time with new wires and coil and it got 10.2mpg

I dont like filling up the truck so I run it 4 days or so and fill it back up. Also with both tanks I averaged 55mph. I am hoping for 13-14mpg with 3.54s!!
1967 mercury F350 7.3 IDI ats turbo kit c6 gear vendor overdrive 3.73s rolling on 19.5s
1971 sport custom on 1979 f350 highboy frame 460 c6 np205 dana 60s 3.54s
1974 F100 baby blue & rust 240 3 speed 3.70s sitting on the ground!
1990 F250 extended cab FI460 e40d 3.55s daily driver
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Re: fuel mileage with 390??

Postby Racer Z on Mon Feb 28, 2011 9:02 pm

I get 10 MPG Highway in my 70 F250. I've got a fresh 390 with C6 and a lumber rack. The 4-barrel carb is getting worn, needs to have the throttle shafts bushed. I've also using an Edelbrock Performer 390 intake with stock "log" exhaust manifolds.

Rear end gearing will effect MPG as will brakes and tires.
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Re: fuel mileage with 390??

Postby Dirty Offio on Tue Mar 01, 2011 12:52 am

my 68 Crewcab gets 14-16 running empty at 50-55 with 4.10's.  (4x4)  

BUT...

When I first bought it, it got 2 1/2 MPG. It had a tired old 360 (2 barrel) that needed a tune up, clutch slipping, with a 14' overhead camper (HEAVY).

Did the tune up (plugs, wires, cap, rotor, points, condenser, air filter) and changed the clutch.  Bumped the mileage to 5.

Bought an electronic ignition conversion kit (Mallory Unilite), put it in and got 7 to 8 mpg.

Put a fresh 390 in (slightly warmed up) with an Edlebrock 4BBL and averaged 10.  IF I keep my size 13 outta the secondaries!  lol

All of the above was with the camper on it.

Pulled the camper out, and it runs 14-16 consistantly, provided I can hold the speed down.  If I get up on the Interstate, the mileage drops to about 9.
When in doubt, hit the gas. It may not be the right answer, but at least it ends the suspense!!
The only substitute for Cubic Inches, is Cubic Money!
1967 F-100 swb "Varmit"
1968 F-250 4dr lwb "Beast"
1976 F-350 drw 460
1977 Club Wagon
1978 Mustang King Cobra
1986 F-250 lwb
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Re: fuel mileage with 390??

Postby fomocoguy on Sun Mar 06, 2011 9:05 am

Dirty Offio wrote:my 68 Crewcab gets 14-16 running empty at 50-55 with 4.10's.  (4x4)  

BUT...

When I first bought it, it got 2 1/2 MPG. It had a tired old 360 (2 barrel) that needed a tune up, clutch slipping, with a 14' overhead camper (HEAVY).

Did the tune up (plugs, wires, cap, rotor, points, condenser, air filter) and changed the clutch.  Bumped the mileage to 5.

Bought an electronic ignition conversion kit (Mallory Unilite), put it in and got 7 to 8 mpg.

Put a fresh 390 in (slightly warmed up) with an Edlebrock 4BBL and averaged 10.  IF I keep my size 13 outta the secondaries!  lol

All of the above was with the camper on it.

Pulled the camper out, and it runs 14-16 consistantly, provided I can hold the speed down.  If I get up on the Interstate, the mileage drops to about 9.

Just curious, what diameter tire are you running?
Joe

1969 F250 Crew Cab 4x4
2000 Jeep Cherokee Classic w/3" lift
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Re: fuel mileage with 390??

Postby 1972hiboy on Mon Mar 07, 2011 2:30 pm

my 72 with 9.00x16's fresh 390 manual trans holley four bbl if I play nice with it, it will do the 10-12 mpg ballpark.....thats around town I dont have enough miles on the 390 to take it on long stints on the hwy yet...oh Ive got 4.11s
Rich
1973 f350 super c/s 460/c6 22k orig miles
1972 f350 srw crewcab special 390
1972 f250 ranger XLT Camper Special 390
1972 f250 4x4 custom 84k og miles 390
1971 f250 4x4 sport custom 56k og miles. 360
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Re: fuel mileage with 390??

Postby Dirty Offio on Tue Mar 08, 2011 12:37 am

fomocoguy wrote: Just curious, what diameter tire are you running?


Running 8.25 R16's.  (35" tall)  I have not run the milage since I put the 265 70R 16's on it.  (it has been under the weather with fuel system problems for a while...but that is a seperate post!  lol)  I wish I could have found another set f those 8.25 R16 Continental's tho, they wore like iron!  Still have them, and the tread is fine, but the sidewalls dry rotted out on them.
When in doubt, hit the gas. It may not be the right answer, but at least it ends the suspense!!
The only substitute for Cubic Inches, is Cubic Money!
1967 F-100 swb "Varmit"
1968 F-250 4dr lwb "Beast"
1976 F-350 drw 460
1977 Club Wagon
1978 Mustang King Cobra
1986 F-250 lwb
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Re: fuel mileage with 390??

Postby Dirty Offio on Mon Jul 04, 2011 1:23 am

Update:  I mistyped on my previous post.  the tires are LT265/70R17, not 16.  I have been running it around both local and interstate lately.  

Local, running back and forth to work (10 miles, mostly 50 MPH road, several stoplights and stop signs, plus 2 roundabouts) it is running about 9 MPG.

running on the interstate at about 65, it is getting 13, so it cost me a couple of mpg to swap to the shorter tires.
When in doubt, hit the gas. It may not be the right answer, but at least it ends the suspense!!
The only substitute for Cubic Inches, is Cubic Money!
1967 F-100 swb "Varmit"
1968 F-250 4dr lwb "Beast"
1976 F-350 drw 460
1977 Club Wagon
1978 Mustang King Cobra
1986 F-250 lwb
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Re: fuel mileage with 390??

Postby woods on Mon Jul 04, 2011 8:29 am

In my 71 4X4 with 411's, 35's and a 428 I get close to 15. However, my engine is built a little "different" than the norm.
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Re: fuel mileage with 390??

Postby 390Nut on Mon Jul 04, 2011 9:45 am

'69 f100 2wd, 390 running 9.5/1CR and a .270 Crower cam, bigger exhaust valves (CJ sized) with dual exhaust (stock manifolds) 4spd, 3.50 gears, was running 235/70R15's and got 10mpg on average.  Got 31x10.5 tires on there now but haven't been driving the truck to know if the mileage changed.
Paul
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Re: fuel mileage with 390??

Postby Racer Z on Mon Jul 04, 2011 12:03 pm

I recently took mine on a 200 mile day trip and got almost 12 MPG.

The spec are: 1970 F250 w/ 390 (fresh, stock) stock exhaust manifolds, Edelbrock Performer 390 intake manifold, Carter 4-barrel (needs work); 9.50 x 16.5 tires; auto; lumber rack. I had a couple of hundred pound of broken concrete in the bed, rode smooth. I sat on 65 MPH. With these tires my speedo is off by 7%, when it shows 70, I'm doing 65. The speedo registered 70 for the trip.

I don't remember if that was with dual mufflers or single. I changed over to single to make room for a camper special fuel tank.
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