I am only getting 7MPG while towing a small snowmobile trailer with two sleds @ 60mph highway driving. Cruise RPM of about 2800RPM

I am running a 72 F250 4x4
With 33" tires
4.10 gears
390 with a little more than stock compression
Headers, Dual 2 1/2" exhaust(back to muffs only)
262 int./270 exh. 0.513 int./0.520 exh. lift Comp cams
Edelbrock Streetmaster intake(soon to be changed with a Performer)
Holley 600cfm vacuum secondary carb
Just this last weekend I messed with the timing and fixed some issues, It is now set @ 10 deg. initial 24 mechanical for a total advance of 34 deg. Full advance by about 2700 RPM
My Vacuum is advancing a total of 18 degrees.
Carb is jetted correct and plugs look good as far as jetting goes.
Truck runs Great, plenty of pull lots of power but I got to get the mileage up. I am hoping for 10(which is crap)
I had a hotter cam in it with a double pumper in it a couple years ago with a quicker advance curve and got 10mpg. I thought changing to this combo would help my MPG and give more torque for towing(which it did the latter)

Any ideas on things to check or change. If I can't get this better I am afraid I will have to get something else.

 

72f2504x4390, Welcome to FTE the nations truck stop for Ford truck tech support.

First thing I would do is get rid of the 4.10. I run a 3.00 behind my 352/C6 and can get 14 and change empty. I turn 2050 @ 55 mph with P 235 70R 15 tires.

You might not want to go to a 3.00 but I pull a tandum axle trailer with it just fine.

That is just too much gear behind that engine unless you are drag racing it. IMHO

John

 

With the tire size difference between mine and yours I would only have to drop to 3.50 gears to match yours.

Problem is, highway I would be fine, but with a 3 speed tranny it just doesn't work pulling up the mountains. I use the truck primarily for pulling the snowmobiles which around here equates to a lot of pulling steep grades at lower speeds. I really need a 5 speed. Maybe that should be my next step.

I do want good take off also, not drag racing but good take off is a must.
Remember this is a 5300lb truck too, not a light weight 2wd.
Thanks for the response

 

I run 3.54 gears with 35" tires and a hopped up 300 I6 and can get 15MPG on the freeway at around 80MPH. I only get about 9MPG in town though. I also snowmobile and pull a 2place over the hills at about 50MPH, I have to grab 3rd @ the steepest spots. With the 3.54 gears, 4th is more of an overdrive anywho. I am currently saving up for the bearings to swap to 4.10:1s. I think it will work better for me for light to light in town and over the hills.

 

Then drop the 3 spd for a C6.

A 72 F100 will pull your light weight trailer load without any issues. Don't come on this forum and go there. Excluding any 4wd issues, I'll match up my 66 F100 2wd with 6,000 lbs hitched against your F250 with the same hitch and run you all day long with it, and be there maybe in front of you at the end.

John

 

A 5 speed would probably help with the overdrive going down the highway, and still lots of gears to downshift to when pulling the hills..... Big thing is a 390 just doesn't get great mileage in a 4X4 with tall tires. Heck, they don't do that great on mileage in a 2wd and flat land towing.... The FE's were designed for making big torque back in the day when the price of gas was cheap enough that fuel mileage wasn't even a consideration....

 

Get a five speed installed, and play with your engine tune some more. I think you can find more mileage in your engine, but most of your gains will come from dropping your cruise rpm's.

My '70 F100 has a 9.5:1 390, Holley 600 vaccuum secondary carb, and a Comp Cams 268H grind. I run about 12 degrees initial timing. It turns a C6 with a stock converter to a 3.50 geared rear turning 31x10.50's, and I can get 15 to 17 mpg from the truck pulling a load similar to yours.

 

see if they make an adapter for a ZF 5-speed to an FE motor. then if they do, then i would use that tranny with 3.54 gears. you'll have a low gear for pulling, and an overdrive to keep the revs down. i would say a properly tuned 390 should get around 15 with this combo.

 

try hooking vacum gauge to carb and try to get it around 25hg and mabey some thiner tires not shorter but thinner. causethe rubber thats on the road is takeing away from gas mileage about 5% is going out in that anoying wrrrrrrr sound when on the road.

 

i pull a 4400 lb camper with my 72 f100 302 and average around 12-13 mpg and get 16 empty. and have never had any issues such as lack of power,overheating,etc. i have been pulling this camper since 1997.