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Gas mileage feedback...

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1986F150Six

Gas mileage feedback...

Administrator

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

Re: Gas mileage feedback...

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;).

1994 F150 4x2 Flareside. 5.0 w/MAF, 4R70W, stock.
1984 F150 4X2 Flareside. Mild 302 w/ 5spd. Sold.
1980 F150 4X4 Flareside. 300i6 w/ 5spd. Sold in 2021.
1980 F100 4X2 Flareside. 351w/2bbl w/NP435. Sold in 1995

FuzzFace2

Re: Gas mileage feedback...

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 ----

Dave G.
81 F100 flare side 300 six / AA OD / NP435 / 2.75 gear
http://cars.grantskingdom1.com/index.php/1980-Ford-F100?page=1
81 F100 style side 300 six/SROD parts truck -RIP
http://cars.grantskingdom1.com/index.php/1981-Ford-F100

Gary Lewis

Re: Gas mileage feedback...

Administrator

In reply to this post by 1986F150Six

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.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

Dorsai

Re: Gas mileage feedback...

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

Matthew
1980 F-150 Custom 2wd longbed, 300-6, C6, 2.75 rear axle
Atlanta GA

Ford F834

Re: Gas mileage feedback...

Administrator

In reply to this post by 1986F150Six

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.

SHORT BED 4-DOOR DIESEL: 1986 F350 4x4 under construction-- 7.3 IDIT ZF5+GVOD

STRAIGHT SIX 4X4: 1981 F150 2wd to 4x4-- 300 I6 close ratio diesel T19, hydroboost brakes, Saginaw steering

BIG F: 1995 F-Superduty under construction— converting to 6.9L IDI diesel ZF5+DNE2

Danny G

Re: Gas mileage feedback...

Ford F834 wrote

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

1986 F-150|Standard Cab|4x2|300Six|C6Transmission w/3.08 rear|Name:TBD
2021 Ranger XLT Super Crew

Danny G

Re: Gas mileage feedback...

I like this tire size guide as well:
https://www.tacomaworld.com/tirecalc

1986 F-150|Standard Cab|4x2|300Six|C6Transmission w/3.08 rear|Name:TBD
2021 Ranger XLT Super Crew

1986F150Six

Re: Gas mileage feedback...

Administrator

In reply to this post by Rembrant

Rembrant wrote

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

Re: Gas mileage feedback...

1986F150Six wrote

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.

Danny G

Re: Gas mileage feedback...

Rembrant wrote

1986F150Six wrote

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.

This is one of the reasons I like that link above it shows a good break down of the tire differences.

1986 F-150|Standard Cab|4x2|300Six|C6Transmission w/3.08 rear|Name:TBD
2021 Ranger XLT Super Crew

Danny G

Re: Gas mileage feedback...

The PO had 235/70/R15 on mine, the door sticker actually reads 195/75 R15 from the factory. But personally I feel like those look very small and out of place on the trucks.

1986 F-150|Standard Cab|4x2|300Six|C6Transmission w/3.08 rear|Name:TBD
2021 Ranger XLT Super Crew

Whisler

Re: Gas mileage feedback...

Anyone have an idea where to find the "torque peak RPM" for my '84 351w (originally 2 barrel not HO)?Then I could use the calculator to see what speed that relates to (or just watch the tach).

God Bless
Whisler

Frankenstein: 1989 F250 4X4, C-6, Hurst Pro-Matic 2 shifter, carbed '84 351W, Edelbrock manifold, Edlbrock AVS, DS2 ignition, 3G alternator, JBA shorty headers, no cats, dual exhaust with H pipe.

Gary Lewis

Re: Gas mileage feedback...

Administrator

Yep, sure do. Probably only one place on the interweb - here!

Go to Documentation/Engines/Windsor and then the 351W tab and then the Specifications tab. And then scroll down to the 1984 spec's.

Gary, AKA "Gary fellow": Profile

Gary Lewis

Re: Gas mileage feedback...

Administrator

In reply to this post by Danny G

That's an interesting calculator. And I was excited when I saw the "embed" info thinking we could embed it here. But, it really isn't embed code and is instead a link.

We have the calculator shown below on the Documentation/Driveline/Calculators tab. And I'm wondering if we should incorporate a tire size calculation in it. Tire size calc's are pretty close, but each manufacturer's tires vary a bit in size, as you can see on the Tire Rack site. But, I think it would be pretty easy to add the tire size calculations to the spreadsheet to allow us to play what-if games.

So, what do y'all think? Would it help?

Gary, AKA "Gary fellow": Profile

Whisler

Re: Gas mileage feedback...

The documentation and the calculator are awesome.

What surprised me, when I looked up my 351W 2V, is the 1800 RPM torque peak. With 3.55:1 gear ratio I am not likely to cruise in that range much.

Then I looked at the 351W 4V and saw that the torque peak was at 2800 RPM. If I am correct in believing that the difference between the 2V and 4V (HO) is carb. and cam, then the cam used in the HO version moved the torque peak 1000 RPM, because I don't see how the carb. change could move the torque peak RPM.

So now, with my C6 transmission, I need an HO cam to move the torque peak so I can cruise at 65 and be in the 2800 RPM torque peak range. Oh DARN!!! (Should have changed the cam while I had the engine out.)

Or I could switch to an AOD transmission with its deep overdrive and cruise at 1800. But that option would be a lot more expensive and troublesome.

"What-if" is sure fun even if you know you will never do it.

Thanks for all your work , Gary.

Gary Lewis

Re: Gas mileage feedback...

Administrator

There are LOTS of variables in play when trying to achieve max efficiency. One is the engine RPM, but not only is the max torque important, but so is the friction loss w/in the engine. MIT has an interesting paper entitled Engine Friction And Lubrication, and in it is this chart on engine friction. As you can see, the engine friction goes up dramatically as the RPM increases. So while you may gain efficiency by the engine operating at max torque, raising the RPM by 55% will certainly increase the friction, and that might negate the gain.

So it is best to get RPM down to a reasonable value AND to get the max torque to coincide with the lowered RPM. But with a C6 you are also battling inefficiencies in it as well. The torque converter doesn't have a clutch so is always slipping, and depending on the load that's usually between 200 and 300 RPM. Not only does that raise the RPM and, therefore, the friction, all of that slippage is turned into heat and is lost energy. Plus the C6 is notoriously inefficient in and of itself. And, it has no OD.

The AOD is a more efficient design as it is based on the C4. Plus, it does have a mechanical lock that bypasses the torque converter, and it has overdrive. And I'm told that it is possible to build one of those to stand up to a strong 351W. But it is expensive to do and you'd have to drive a lot of miles to make it pay off.

Gary, AKA "Gary fellow": Profile

85lebaront2

Re: Gas mileage feedback...

Administrator

Gary, that was the secret to the old Mercury Turnpike Cruisers, big engine (368 ci in 1957, 430 in 1958-59), 2.69:1 rear. Engine was only turning around 1700 rpm with the Merc-O Matic or Cruise-O-Matic transmissions. Another item to consider, stroke length, longer stroke = more friction losses, which is why a 302 vs a 300 in a truck, highway usage, the 302 has it all over the 300 with the same drivetrain. Granted the total linear travel is the essentially same 8 pistons at 6" per revolution or 6 pistons at 7.96" per revolution is 48" vs 47.76". Due to the angularity of the 300 connecting rod to the piston at mid stroke (it's bad enough that performance builds sometimes use 240 rods and special pistons) creates a lot of side load compared to a 302.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

Danny G

Re: Gas mileage feedback...

In reply to this post by Gary Lewis

Checked out that spec page... Got to love that low end torque on the 300 six. 1986 numbers showing 250ftlbs at 2000 rpms, 245 at 1800 and still... 240 at 1200 rpms. That means if you got your gear/tireset up and transmission in OD to where you were running at 1200 rpms you are still getting 240ftlbs of torque while sipping fuel. With the EFI donor engine I have and I would expect a bit more.

Couple that with a E4OD, my 3.08 rear and some 30 inch tires and at 55mph your supposedly cruising at 1350rpms. If you use an AOD it would be a bit different as the AOD is a 0.67 OD vs the E4OD's 0.71.

If you wanted to get silly, same set up with a gear vendors unit (double OD of 0.55) at 65mph drops the rpms to 1233, or change the rear to 3.55's and be pushing about 1450rpms at 65mph with that double over which is about what the E4OD would do at 55mph on its own.

1986 F-150|Standard Cab|4x2|300Six|C6Transmission w/3.08 rear|Name:TBD
2021 Ranger XLT Super Crew

1986F150Six

Re: Gas mileage feedback...

Administrator

Or, do as Ford did for stellar gas mileage... put a 2.47 rear end with manual OD!!!