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Gas mileage reporting [4.9L w/ manual O.D. and 3.08 rear gears]

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1986F150six
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Gas mileage reporting [4.9L w/ manual O.D. and 3.08 rear gears]

Post #1 by 1986F150six » Tue Sep 18, 2018 3:39 pm

Well, I am back from the 2018 Garagemahal Ford Truck Show in Skiatook, OK [what a great time to be had by all who attended!!!].

I attended in 2017, but due to mechanical problems with my truck, was unable to drive it.

I decided to update this older thread by including the gas mileage for this year in the same format as before. Since the previous listings, the distributor has been replaced with a NOS Motorcraft Duraspark distributor which was recurved by WSA111. Bill asked if I might be interested in slightly better performance and gas mileage, but would be required to use 89 octane gasoline. I agreed and the static timing is @ 16* BTDC.

This year, I decided to drive to get there as quickly as possible and drove the speed limit or with the traffic flow [faster].

Instead of my "normal" tank-by-tank description, I am going to provide the overall average for the approximately 1200 mile trip as compared to the previous 3 years.

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]

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THE FRENCHTOWN FLYER
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Re: Gas mileage reporting [4.9L w/ manual O.D. and 3.08 rear gears]

Post #2 by THE FRENCHTOWN FLYER » Tue Sep 18, 2018 4:57 pm

Thanks 1986F150six.
Good useful data to digest, and answers the most frequently asked questions regarding vehicle aerodynamics and vehicle speed.
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Re: Gas mileage reporting [4.9L w/ manual O.D. and 3.08 rear gears]

Post #3 by arse_sidewards » Wed Sep 19, 2018 7:51 am

1986F150six wrote:Well, I am back from the 2018 Garagemahal Ford Truck Show in Skiatook, OK [what a great time to be had by all who attended!!!].

I attended in 2017, but due to mechanical problems with my truck, was unable to drive it.

I decided to update this older thread by including the gas mileage for this year in the same format as before. Since the previous listings, the distributor has been replaced with a NOS Motorcraft Duraspark distributor which was recurved by WSA111. Bill asked if I might be interested in slightly better performance and gas mileage, but would be required to use 89 octane gasoline. I agreed and the static timing is @ 16* BTDC.

This year, I decided to drive to get there as quickly as possible and drove the speed limit or with the traffic flow [faster].

Instead of my "normal" tank-by-tank description, I am going to provide the overall average for the approximately 1200 mile trip as compared to the previous 3 years.

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]


This sounds about right. My stock height '94 with E4OD, 3.08s, 31s, 4x4 and missing the stock plastic under the bumper routinely got ~20-21mpg on highway only drives at 55-70mph.
1994 F150 4x4 8ft, engine is basically stock.

66" leafs, extended radius arms, lockers in both ends, nothing special.

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Re: Gas mileage reporting [4.9L w/ manual O.D. and 3.08 rear gears]

Post #4 by 1986F150six » Wed Nov 27, 2019 8:17 am

Update:

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].
1986 F150 4.9L manual O.D. 3.08 Duraspark MSD ignition w/ no EGR

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Re: Gas mileage reporting [4.9L w/ manual O.D. and 3.08 rear gears]

Post #5 by THE FRENCHTOWN FLYER » Wed Nov 27, 2019 11:17 am

Do you happen to know what the intake vacuum and A/F ratio was at 50 and 70?
Perhaps at 50 the intake vacuum was low enough to open the power valve but it was high enough to induce additional pumping losses (at 50 vs 70)?
Any chance the electrical and/or A/C loads varied significantly?
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Re: Gas mileage reporting [4.9L w/ manual O.D. and 3.08 rear gears]

Post #6 by arse_sidewards » Wed Nov 27, 2019 11:41 am

THE FRENCHTOWN FLYER wrote:Do you happen to know what the intake vacuum and A/F ratio was at 50 and 70?
Perhaps at 50 the intake vacuum was low enough to open the power valve but it was high enough to induce additional pumping losses (at 50 vs 70)?


This is my bet. His results are opposite of mine with an almost identically geared truck and EFI.
1994 F150 4x4 8ft, engine is basically stock.

66" leafs, extended radius arms, lockers in both ends, nothing special.

1986F150six
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Re: Gas mileage reporting [4.9L w/ manual O.D. and 3.08 rear gears]

Post #7 by 1986F150six » Wed Nov 27, 2019 12:08 pm

THE FRENCHTOWN FLYER wrote:Do you happen to know what the intake vacuum and A/F ratio was at 50 and 70?
Perhaps at 50 the intake vacuum was low enough to open the power valve but it was high enough to induce additional pumping losses (at 50 vs 70)?

No, Sir. I can tell you that @ 50 mph in OD, even small rises are greeted with a moan [not lugging] as the throttle opens to maintain speed. At 55-60 mph, the same throttle movement results in acceleration without the moan.

Any chance the electrical and/or A/C loads varied significantly?


I drive to be comfortable, so use A/C or defroster [compressor energized] as needed. On the latest 50 mph Natchez Trace drive, the defroster was being used most of the time due to rainy conditions and two warm bodied men fogging the glass. :oops:
Last edited by 1986F150six on Wed Nov 27, 2019 1:49 pm, edited 1 time in total.

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Re: Gas mileage reporting [4.9L w/ manual O.D. and 3.08 rear gears]

Post #8 by old28racer » Wed Nov 27, 2019 1:14 pm

What kind of aerodynamic are you talking about?

As FTF asked do you run a vacuum & AFR gauge when driving?

What size power valve do you run?

What intake & carb are you running on your 300 4.9L?
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1986F150six
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Re: Gas mileage reporting [4.9L w/ manual O.D. and 3.08 rear gears]

Post #9 by 1986F150six » Wed Nov 27, 2019 1:51 pm

Look over this thread and it will tell what has been done as well as what carburetor, distributor, etc. At the very end is a photo of one aerodynamic variation [simple, but effective].

https://www.ford-trucks.com/forums/1325 ... 300-a.html

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Re: Gas mileage reporting [4.9L w/ manual O.D. and 3.08 rear gears]

Post #10 by old28racer » Wed Nov 27, 2019 11:50 pm

A couple of things I would like to ask. I also run a vac & wide band AFR in my 300 4.9L in my 1971 F-250 with 3.73 gears and a C4 trans. 8.75 R16.5 tires at 60#.

You say in the thread you sent me that your warm idle AFR was around 12.0. My current warm idle AFR is 14.6. 12.0 seems very rich. Your 60mph cruise in mid 15's looks very good, I would like 15.5-16.0 on my rig if I can.

One big difference on yours & mine is you are running a YF carter 1bbl on a stock 1bbl intake and I am running a Holley 2300 350 cfm 2bbl with a 1x2 carb adapter on a stock 1bbl intake.

I am just getting started on mileage improvements. In order they are as follows.
Convert points distributor to a Protronix Ignitor 1 with flame thrower coil.
Open current Motorcraft plugs to .045 gap.
Mill out stock 1bbl intake hole to a 2bbl hole.
Retest my 45-50 cruise AFR.
Replace the stock pair 61 jets with 57/55 or smaller jets.
Get my 45-50 cruise AFR at 15.5-16.0

I may in future change carb to a Autolite 2100 / 2150 2bbl, best 2bbl carb Ford ever built.

I currently get 15.6 mpg highway witch is not to bad for my setup, but my town mileage is real poor at 8-9 mpg. Shooting for 19-20 highway and 12-14 around town. I will never get what you get with the YF carb, they are great mileage carbs. Thanks for your time.
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Re: Gas mileage reporting [4.9L w/ manual O.D. and 3.08 rear gears]

Post #11 by Harte3 » Thu Nov 28, 2019 11:45 am

The best mileage at 55-62 has been my experience with several vehicles at about 1800-2000 rpm. The last big truck I drove before retiring had 2.73 rears and a 13 speed .74 OD tranny behind a 565 hp Cummins would not cruise well at all at 55 in OD but did just fine in direct.
'83 F150 300, 0.030 over, Offy DP, Holley 4160/1848-1 465 cfm, Comp Cam 260H. P/P head, EFI exhaust manifolds, Walker Y Pipe, Super Cat, Turbo muffler, Recurved DSII, Mallory HyFire 6a, ACCEL Super Stock Coil, Taylor 8mm Wires, EFI plugs.

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