Hopefully this thread won't launch a round of liars poker. If you have actually calculated your mileage please post up the numbers and some specifics about the drivetrain combo and conditions you calculated the mileage number you are posting. Whether you have a stock flathead or a 500HP engine I'm curious of the real mpg capability. These trucks have the aerodynamics of a brick so it's a challenge to approach the mpg of the donor vehicle.

I have a 53 F100 with a carbed 302 , 3.90 gears and a C4. I think 13mpg is an honest average number. Maybe I am dreaming but I'd like to see 15-16 mpg so I can expand my summer cruising range when gas prices spike. Perhaps EFI or an OD is in my future but my current combo is dead reliable and I think the upgrade return on investment is very long so for this winter I plan to....

-Replace the 3.90 gears with 3.23s I have on the shelf
-Rejet the Edelbrock Performer carb a bit leaner as I know it is a little fat from reading my plugs.
-Replace my junk 80s truck low compression emission heads with milled E7s for a half point CR increase.

So let's hear your mpg numbers, and a comment on my plans if you care to.

 

I've got a '54 with 302/AOD out of a 90 Mustang. The 302 is converted to a carb and running a Holley Street Avenger 570. I've got the stock 4.10 rear gears and I'm getting right at 17 on the highway and it does better at 65 than 75.

I plan to swap to a 9" and probably 3.70 or 3.50 gears at some point, but I don't expect a big jump in MPG because, as you say, the aerodynamics of a brick don't help much...

 

In my panel I've been consistently getting 22½ to 23 mpg highway based on the imperial gallon. It has a stock 5.7L with vortec heads, Holley Stealth Ram MPFI , 700r4 trans and 3.08 rear end gearing. Next spring I'm going to take in and have it dyno tuned to get it running top notch. Took the panel over the scales and weighs in at 4500 lbs

 

My 53 is running a 5cyl. Mercedes diesel with a direct drive auto trans. and 3:27 gears.Empty I run a consistent 20 MPG and on a 15K trip to AK pulling my 1600lb. teardrop camper I averaged 18.2.

 

I just happened to check my F1 today for the first time, 14.3 MPG. Checking the mileage in the past, the F100 was 14 MPG also.

1951 F1
84' 302 stock internals -
edelbrock carb
performer RPM intake
exhaust manifolds with duels
AOD trans
9" - 3:70
235-75-15 rear tires

1955 F 100
84' 307 Oldsmobile stock internals
stock intake factory quadrajet
exhaust manifolds with duels
2004r trans
10 bolt 3:73
235-75-15 rear tires

 

Stock 226 with 3.92 chunk and I get about 10. But I live in the mountains.

JB

 

I tracked my mileage and calibrated my speedo on the trip to Truckstock. 3,290 miles, 214 gallons. That averages out to 15.4, including the downhill run out across the plains, climbing the hills in KY and TN, and climbing back to Albuquerque. I was running mostly 60-65 mph on the open road. Around town I usually get about 14, although that varies widely.

The sweet spot for mileage appears to me (for my combination) to be 55, but running at 70 for a tankful only dropped mileage about 0.5 mpg.

 

You can subtract 20% to get your mpg in US gallons, so you're getting 18-18.4 MPG - pretty good!

That 4500 lbs sounds heavy though...

 

Thanks everyone for posting. It was interesting to hear what the EFI/OD combos were getting. There were not a lot of them on the board when I used to post here regularly. I expect there may be some forum pickups getting low 20s on the highway. 56panelfords mileage is very good. There are a lot of modern SUVs near that weight that don't do that well on fuel.

 

Ross, what rear gear are you running?

 

I have a 9" with 3.50 gears

I'm still tuning, and hope to bump that cruise mileage up a couple mpg

 

Keep us posted. Any further gains best I have ever heard of from a flatty. You're already going great. Way below 15 is pretty typical with factory gears as I'm sure you know. What is the vintage of the Rochester carb you are using?

 

So far mostly just fooling around in town , but based on how fast the tank empties I would have to say AWFULL . I dont care it's fun!!

 

The Rochester is for a 63 Chevy pickup with 283.

I beg to differ on this being the best for a flathead. When driving with Doc and his father to Truckstock, say 25% mountains, 25% city, and 50% highway, Doc's stock truck and his father's stock V8 shoebox both took within tenths of a gallon as what I did to refill at gas stops. The shoebox was loaded to capacity, or it probably would have done better than the trucks.

On that trip I had to go up two jet sizes from my Albuquerque tune as I dropped down in altitude. I was showing air/fuel ratios in the 17s at one point, got scared and just went a bit fat. I can do better.

 

Please just accept it as the compliment I intended it to be. 15 mpg is very good, 17 you are targeting is outstanding. 10-12mpg is more typical for a flatty. Less than that if you have stump puller gears. 1990s EFI trucks got 15mpg most of the time. You're doing very well. If I am wrong then other flatty owners will be along soon enough.

And provided you are not experiencing any detonation, 17-1 AFR is not a big deal at typical low load cruise on a low compression engine that I assume you have. Some engines won't run well there but many will. That's where peak mpg may happen. Wide open throttle is an entirely different situation of course. And so is detonation if it is happening at any load %.