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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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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.

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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?
Bad Day Racing Is Better Than A Day In The Stands :mrgreen:

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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.
Bad Day Racing Is Better Than A Day In The Stands :mrgreen:

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

Post #12 by 65 F-100 pete » Tue Dec 31, 2019 6:41 am

Hello Harte3,
You and I chatted on Ford Truck Enth. 4 yrs. ago? At that time I was looking into taking off the stock exh. mnfld. & replace that with split cast iron mnflds.
I have now done that. I made an aluminum exchanger out of a 1" thick piece I had. I made it the approx shape of where the old mnfld was. Complete with the three holes to bolt it up to the intake. I drilled a hole all the way thru it, ( hole parallel with the 6 cylinders ). The hole was the size appropriate for tapping each side with the 3/8" NPT. Then nipples and heater hoses.
It is working. I am really impressed with what a difference this improved breathing has made.
Thank you for your help. I too have stopped working for others. My job now is drawing/planning a 24'x24' "hobby shop" here. I am finding having a routine every day is making the transition a help. I do not have a set get up time. Today, I awoke ar 3:06. I got out of bed at 5:00.
Awe righty then, Happy New Year Sir, Pete

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

Post #13 by xctasy » Tue Dec 31, 2019 8:34 pm

The general frontal area verses BSFC for 2800 pound truck with frontal area is run off the Index of Efficiency



Image.

The Y = mx-1 formula works for this. Weight is a minor factor at constant grade and speed, its influence goes up with grade.

For gearing, use the Snook formula.

I've studied this at length and have three answers. Through the discipline and information on these old Ford and Fox engine combinations, the Corporate Average Fuel Economy (CAFE) average fuel consumption figures showed that it is possible to do a fuel consumption prediction for flat roads.

It was here that I learned there are many primary factors for mileage.

Power to weight ratio
Engine tune (Idle speed influences, ignition, HP per liter)
Gear ratio, tires, and aerodynamics
Climate (warmer climate uses less fuel)
Driving style (getting optimum mileage takes skill)
Terrain (flat terrain gets a lot better mileage than hilly terrain)

I have a computer simulator which calculates field US miles per gallon given some basic details. I've used it to forecast different miles per gallon for different engine combinations. And then backed it up by real-world testing.

It stems from an argument that arose in the early 80's when Chrysler Australia sold a four 1.6, 2.0, 2.6 and 4.3 liter sedans, and they all got the same real world fuel economy figures. Wheels May, 1980 found no difference in 2.6 vs 2.0 fuel consumption, and then the blunt old 3200 pound 4.3 liter Electronic Lean Burn CM Chrysler Valiant posted US 26.4 mpg (33 imp mpg) at 62 mph and used to get 21 US mpg (26.2 imp) city to higway.

Image

The adds in Australia and the United States were crazy. Fords Mustang 2.3 with T5 got 38 mpg at 55 mph,
Image

while the Aussie 3.3 Cortina got 28.2 mpg US (35.3 imp) at 62 mph

Image

Ford Cortina verses Sigma verses Falcon verses Valiant fuel economy wars were extinguished when the Total Economy run came out.

adds


The three points are:-

1. In 1978, Ford started responding instantly to CAFE regulations by making its cars

a) 20% slicker through the air (better coefficient of drag, reduced frontal area through downsizing, 400 hours of wind tunnel design for every new design from 1978 on-wards), and
b) over gearing everything 25%.

The aerodynamics results in a huge reduction in engine power needed at speed, and at 65 mph, a 25% reduction in engine revs needed results in a 8% reduction in fuel use. So SROD's, 5 speed over drives, and the Fox body automatics with Moon Shoot gearing were how Ford got the 25% reduction in engine revs. This was the era of the 25% (0.81 and 0.79 in the SROD 4 and 6 and T5), 39% (0.72 in the SROD V8) and 49% over drives (0.67 in the AOD 4 stage), and a 50% overdrive is enough to save 15% in highway miles per gallon.

Ford did this because maximum fuel economy happens when gearing and capacity is optimized to the car... a modern Chevy, Ford or Mopar 6 liter capacity engine can match a 4.2 if its geared right, and the Corporate Average Fuel Economy figures 1981 5.8 LTD got better economy than the 4.2 or 5.0 LTD.

2. Due to the need to mandate stoichiometric air fuel cruise ratios in the Federal high way and city emissions cycle, some 1, 2 and 4 bbl carb engines seem to do better than EFI for MPGS on certain engine combinations (300cube /4.9liter F100 and F150's verses a 4.9 EFI or 5.0 carb or EFI spring to mind), especially when there is a 4-bbl or EFI with 30 or 65 more hp...In the old days before closed loop and open loop EFI, some 1 and 2-bbl engine combinations met the Federal emission manually at leaner than 14.7 or the oxygenated 15.2:1 that is stochimetery, and this allowed them to stay out of the later 12.5:1 open loop air fuel ratios. The modern 3 way cat, feedback system on oxygenated fuel doesn't hurt the fuel economy one bit, but they have some inbuilt limits the old engines don't, and occasionally, the later EEC managed engines suffer just as many in-service problems as the early 1978 to 1982 engine. After 1983 in all states, feedback non lean burn engines became mandatory, even if they were called ELB, High Swirl, or Lean Burn, they weren't ever lean burn again because 14.7:1 became the ideal air fuel ratio. EFI engines can run at 22:1 in low load situations if the exhast valves are tough enough, but the electronics after 1983 forced car makers to adopted non lean burn air fuel rations, and so every engine is 10% less efficiecnt than a non emissions, lean burn engine. So some of those 1978 to 1982 engines could really fly great fuel numbers

3.The ideal gearing for economy was cracked back in th 50's but we had to wait till the late 70's and early 80's for the formula to be re-arranged for best miles per gallon for a given average cruise speed. It is based on the from the Index of Thermal Efficiency, found in French Grand Prix and English RAC litrature by Hodges,

and was revised in 1980 for the Australian Total Economy Run, to use the average frontal area and drag fact for a late seventies, early 80's car. See http://www.snooksmotorsport.com.au/index.php?option=com_content&task=view&id=31&Itemid=39

Here is my computer out put for a 3.3 and 4.1 engine in a Fox Mustang, using the Snook variation on the Index of Thermal Efficiency


Image

xctasy wrote:You can calculate it for any pre 1983 passenger car without a wind cheater body.

The method eliminates different frontal areas, tire drag and variable drag co-efficients, and is based on a coarse chip road surface, so it works for non wind cheeter boxy Mustangs, Falcons and sedans and wagons driven in non freeway conditions.

mpg@62mph =* 1/(140 L/M act + 0.006W + 5)*100*2.2588
*********************** 3.540062

Where:*** L = the engine swept volume in liters, calculated as follows:
******************** Bore in mm*Bore in mm*Stroke in mm*No of Cylinders*0.78543691
************************
************** M act = mph per 1000 rpm in the highest available gear, using normal driven wheel tire*
********************* placard details as follows:
**************************** ****************** ****************
*******************(Tire section*Aspect ratio as decimal)+(Tire section*Aspect ratio as decimal)+Wheel diameter in inches*25.4
1.022
******** Then multiply the result by 3.141 * 60, then divide by the diff ratio, and multiply by the top gear ratio

********************* Note: If automatic, 15% allowance for slippage was allowed for automatic transmissions,
********************* and the result of M is multiplied by 0.85.
This is because a T5 and 7.25 to 9" diff takes 26.5% power from the engine,
a C4 and 7.25 to 9" diff takes 31%. Difference in power loss from a manual to an automatic is usually 0.85

*************** W = weight of the vehicles in pounds, plus the ballasted weight of the
*********************** one driver and same weight passenger (200 +200 pounds and full tank of advertised fuel US Gals times 6.073 pounds).
Divide by 2.2046223


Those figures above for

the 1981 3.3 Mustang SROD 4 speed , 3.08:1 diff, 0.81:1 top gear( overdriven )= 28.5 US mpg at 62 mph on a 2.49:1 overall final drive
the 1981 3.3 Mustang C3 Auto 3 speed , 2.73:1 diff, 1:1 top gear =24.7 US mpg at 62 mph on a 2.73:1 overall final drive
the planned 1981 4.1 Mustang AOD 4 speed , 2.73:1 diff, 0.67:1 top gear = 27.2 US mpg at 62 mph on a 1.83:1 overall final drive



That last one is like a 1979 to 1982 4.2 V8 with a 1.83:1 diff ratio. If it was lowered to the factory 2.47 or 2.26, and rerun with a 4.2 engine, the fuel consumption at 62 mph would be 22.4 or 23.7 mile per US gallon at 62 mph.

I re-ran it with the 4.2 4-bbl and AOD with 3.45 diff and got 23.4 US mpg at 62 mph. Image


The above Capri 4.2 with AOD combo with a 2.31:1 overall final drive would have done pretty well.

The lock-up clutch sure would have helped too. If you can employ the lock-up, there is a potential saving beyond that, maybe an extra mpg at 62 mph.

Oh, and a 2.3 with T5 running just a 3.45:1 diff gets 38.6 mpg at 62 mph using the same information. The point is that as an engine gets bigger, it can carry higher gearing, and to do that, the camshaft duration and lift can get dropped. A 4.2 runs 244 degrees of duration and has maximum power and 195 lb-ft of torque at 2200 rpm, which is very low in the rev range. At 100 mph, its only turning 3400 rpm with 2.47:1 gears, so its perfectly geared for 115 hp.

It comes from the above formulae above, and it works.
Image
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