Gas mileage feedback...

[1986F150Six]

Since March of 2008, when I bought my truck from the original owner, I have recorded gas mileage for every tank. Back in 2014, I made my maiden voyage to Skiatook, OK and used the extended trip [~600 miles each way] as a test. The following is a brief summary:

2014 55-62 mph with no aerodynamic modifications = 21.93 mpg [highest tank = 23.26 mpg]

2015 55-62 mph with aerodynamic modifications = 24.13 mpg [highest tank = 25.72 mpg]

2016 55-70 mph [weighted towards 65-70] with aerodynamic modifications = 22.05 mpg [highest tank = 23.46 mpg]

2017 Missing data due to having driven another vehicle.

2018 65-75 mph [closer to 75] with no aerodynamic modifications] = 19.87 mpg [highest tank = 21.3 mpg]

2019 65-75 mph with aerodynamic modifications = 21.65 mpg [highest tank = 21.95 mpg]

2019 60-75 mph with partial [aerodynamics going, but not returning] aerodynamic modifications = 19.12 mpg [highest tank = 21.17 mpg]

Last week, Robert Evans [my friend who accompanied me to Skiatook, this year] and I planned a breakfast run to Tupelo, MS, via the Natchez Trace. This would give an opportunity to drive at 50 MPH [speed limit] and see what the gas mileage would be. There is a gas station very near the entrance, so the tank was filled and refilled at the same pump. The results were disappointing to me, but showed that going too slow [RPMs lower than maximum torque] results in reduced gas mileage since the engine is below its "sweet spot".

50 MPH = ~1400 RPMs

135.7 miles / 6.883 gallons = 19.72 mpg.

So, driving @ 50 mph, the truck returned almost exactly the same mileage as it did @ 65 -75 mph [see the 2018 Skiatook trip results; above].

[Rembrant]

That's great mileage for a Bullnose David. You're running the factory 4 spd w/OD correct? What about rear end gear ratio? Just curious.

I'm hoping to crack 20 MPG with my Bull next spring/summer. I managed to hit 18.25 MPG last year, and this year was still hitting 15+ MPG with a poorly performing engine (AFR off, and various vacuum leaks, etc).

With my vacuum leaks all fixed up, a *new* freshly recurved distributor on the way, and my carburetor dialed in better (along with a functioning AFR gauge), I'm hoping I can crack the magic 20MPG mark. I will more than likely be replacing the 600CFM Holley with the 500CFM Summit carb between now and next spring. It's low (very low) priority at the moment.

The 5spd and 3.08 gears are nice for the highway, so that's a plus for MPG.

The lowly 302 doesn't get much love in the truck world, and I often hear about how it's low torque matched up with a heavy truck is a bad mix, but the truth is my truck weighs about the same as a fully loaded fox Mustang, so it's not a bad match up in reality. I don't have that nice low RPM torque of the 300/6, but the 302 has other redeeming qualities to make up for it;).

 

[FuzzFace2]

That's great mileage for a Bullnose David. You're running the factory 4 spd w/OD correct? What about rear end gear ratio? Just curious.

I'm hoping to crack 20 MPG with my Bull next spring/summer. I managed to hit 18.25 MPG last year, and this year was still hitting 15+ MPG with a poorly performing engine (AFR off, and various vacuum leaks, etc).

With my vacuum leaks all fixed up, a *new* freshly recurved distributor on the way, and my carburetor dialed in better (along with a functioning AFR gauge), I'm hoping I can crack the magic 20MPG mark. I will more than likely be replacing the 600CFM Holley with the 500CFM Summit carb between now and next spring. It's low (very low) priority at the moment.

The 5spd and 3.08 gears are nice for the highway, so that's a plus for MPG.

The lowly 302 doesn't get much love in the truck world, and I often hear about how it's low torque matched up with a heavy truck is a bad mix, but the truth is my truck weighs about the same as a fully loaded fox Mustang, so it's not a bad match up in reality. I don't have that nice low RPM torque of the 300/6, but the 302 has other redeeming qualities to make up for it;).

Besides the rear gear what size tire you are running and the RPM "sweet spot".

Because I did not have a speedo I was trying to judge speed by the tach but don't know how good that is because some of the numbers I was playing with just did not seam right to me for the speed?

Dave ----

[Gary Lewis]

Glad you had fun, David. Tell Robert hello for me.

As for the MPG, you are right about the sweet spot. I assume your 1:1 gear would have had you turning too fast?

Still, that's very good mileage.

[Dorsai]

Glad you had fun, David. Tell Robert hello for me.

As for the MPG, you are right about the sweet spot. I assume your 1:1 gear would have had you turning too fast?

Still, that's very good mileage.

As someone who did not break 14mpg on his drive to Skiatook, I remain in awe of your mileage.

[Ford F834]

Thanks for sharing David! I suspect that your speed was a bit too slow for your overdrive gear, and you were below the sweet spot for mpg. But I also have to ask, do you know if the fuel blend has changed in your region between September and November? I hear a lot of chatter about winter blend fuels hurting mpg, but it is hard to sift through what is fuel related vs longer warm up times, idling, and worse rolling resistance if there is “weather” on the roads. I’m just throwing fuel blend out there as a possible variable.

[Danny G]

Thanks for sharing David! I suspect that your speed was a bit too slow for your overdrive gear, and you were below the sweet spot for mpg. But I also have to ask, do you know if the fuel blend has changed in your region between September and November? I hear a lot of chatter about winter blend fuels hurting mpg, but it is hard to sift through what is fuel related vs longer warm up times, idling, and worse rolling resistance if there is “weather” on the roads. I’m just throwing fuel blend out there as a possible variable.

I think everyone should be running winter blend about now lol.

Having the RPM "Sweet Spot" is good information. You can use a speed/tire/gear ratio calculator to find out what combination will get you in that range.

Much like this one from summit:

https://www.summitracing.com/newsandevents/calcsandtools/gear-ratio-calculator

 

[Danny G]

Thanks for sharing David! I suspect that your speed was a bit too slow for your overdrive gear, and you were below the sweet spot for mpg. But I also have to ask, do you know if the fuel blend has changed in your region between September and November? I hear a lot of chatter about winter blend fuels hurting mpg, but it is hard to sift through what is fuel related vs longer warm up times, idling, and worse rolling resistance if there is “weather” on the roads. I’m just throwing fuel blend out there as a possible variable.

I think everyone should be running winter blend about now lol.

Having the RPM "Sweet Spot" is good information. You can use a speed/tire/gear ratio calculator to find out what combination will get you in that range.

Much like this one from summit:

https://www.summitracing.com/newsandevents/calcsandtools/gear-ratio-calculator

I like this tire size guide as well:

https://www.tacomaworld.com/tirecalc

 

[1986F150Six]

That's great mileage for a Bullnose David. You're running the factory 4 spd w/OD correct? What about rear end gear ratio? Just curious.

Yes, 4 speed manual OD.

3.08 rear gears with limited slip.

215/75 X 15 "road" tires.

FuzzFace2: "Besides the rear gear what size tire you are running and the RPM "sweet spot"."

The highest gas mileage, without aerodynamic assistance, is when the truck is driven 55-62 MPH. Those speeds correlate to ~1530-1730 RPMs.

Gary: "I assume your 1:1 gear would have had you turning too fast?"

I do not know? In earlier in-town testing, where I run my normal commute to work and never go over 45 MPH, eliminating OD for the full tank results in a 2 mpg drop. This test was repeated and returned the same results. That would be due to pumping losses, I believe.

Jonathan: "But I also have to ask, do you know if the fuel blend has changed in your region between September and November? I hear a lot of chatter about winter blend fuels hurting mpg, but it is hard to sift through what is fuel related vs longer warm up times, idling, and worse rolling resistance if there is “weather” on the roads. I’m just throwing fuel blend out there as a possible variable."

Yes, we have the winter blend formulation and through the years, due to all the reasons you have listed, the gas mileage has been noted to be ~1.5-2.0 mpg lower during the winter season.

 

[Rembrant]

215/75 X 15 "road" tires.

Interesting! They are the same size tire that was on my 1984 when it was new. The cool part for me is that the much larger (wider, actually) tires that I'm running now (275/60-15) are actually the same OD as the original 215's. So, while they are much heavier by comparison, they actually kept my speedometer correct to within 1%.

I know they will hurt my fuel efficiency, but I like them enough they're worth the "cost" to me.