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MPG experiment... [4.9L/300 engine prefers low revs]

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1986F150six
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MPG experiment... [4.9L/300 engine prefers low revs]

Post #1 by 1986F150six » Tue Mar 11, 2014 1:45 pm

I retain fuel consumption records reflecting my very reproducible weekly driving pattern. This is for a 1986 F150 with 4.9L engine, 4 speed manual overdrive, 3.08 rear gears, 215/75 X 15 tires, Duraspark conversion and I drive for economy.

I drive 5 days a week to and from work. I live in and pass through another town with 25, 35 and 45 mph speed limits and numerous stop signs and traffic lights. The final 6-7 miles before work is 45 mph farm land. Two lanes and very peaceful. On the weekends, the truck is used for errands, but not much driving.

My average is 16.5-17.5 MPG.

Three seperate times, I have tried the following experiment: Everything remains the same, except during the 6-7 mile drive @ 45 mph, instead of using overdrive [.71:1], the transmission is kept in 3rd [1:1]. At 45 mph in O.D., the engine revs @ ~1200 RPMs and if under light throttle and flat roads, does not lug. At the same speed in 3rd gear, the tachometer indicates ~1700 RPMs.

The average for the three tankfuls used during the test periods dropped by ~2 MPG.

While growing up and learning from a mechanical mentor, who used to compete in the Mobil Gas Economy Run, driving a 1962 Corvette with mechanical fuel injection [327 with 365 horsepower], I was told to upshift as quickly as possible and get into high gear. He had many trophies to back up his ideas.

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #2 by THE FRENCHTOWN FLYER » Tue Mar 11, 2014 3:06 pm

Nothing you've mentioned surprises me, having owned an '85 300.

I don't see a question there, but if you are asking "why did my mileage drop when driving in 3rd gear instead of driving in OD" it is because the pumping losses associated with having a higher intake manifold vacuum used more fuel, combined with higher frictional losses of spinning all the rotating components faster.

Sometimes those losses are offset by the fact that power enrichment circuitry in the carb gives a fatter A/F ratio at lower vacuums. But your feedback carb was probably operating in closed loop mode in either case, so that may not have been a factor.
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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #3 by BIG 6 farmer » Tue Mar 11, 2014 4:47 pm

x2 on not surprised :nod: my thinking is a 300 six, stock or set up for lower speed torque. Will make best MPGs @ ? 1500-2000? RPMs. But only with a light load & speed. Driving with a vacuum gauge, so not to lug it too much so your power valve opens... ( that is for a Carb. that has a power valve. And you would have to know the opening point.) I think a Air/Fuel ratio gauge would be a great tool to drive with for max MPGs :hmmm: In my opinion, (and many others) A properly set up and tuned Carburated Engine, can and has got better MPGs. Than the same Engine with different types of Fuel injection.
83 F 150 SB 4x4 300 six NP 4speed - - 1950 IHC L162 (1&1/2 ton?) - 87 & 88 T-Bird Turbo Coupes - 2000 Triumph Tiger , 76 Honda GL 1000 , & other toys and parts (& junk) -

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #4 by arse_sidewards » Tue Mar 11, 2014 7:38 pm

OP's results are consistent with my experience in a 94 with the E4OD, 3.05 gears and 31s, my aerodynamics are terrible (lifted and missing front air dam). My commute is small hills at 40-70mph with some stop and go. I leave hubs locked (because it's winter and I off-road often enough to make unlocking them inconvenient). I spend a lot of time at 70-90% throttle in the bottom of 4th and while commuting I generally drive with a lead foot. I get about 14mpg. For awhile I tried commuting with OD off (I'm always on the throttle so the extra drag while coasting almost never came into play) and got 12mpg no matter what I did.
1994 F150 4x4 8ft, engine is basically stock.

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

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #5 by J.R. » Tue Mar 11, 2014 9:35 pm

Had a boss with a bare-bones 1965 F100, 300” six, 3-on-the-tree (maybe w/BW overdrive?), stock light duty tires, short bed & cab-high shell. He drove highways @ 55mph & got 24mpg average with his ‘little-old-lady’ driving style. No tach, but we guessed that he was right @ the engine’s 1800rpm torque peak for most miles.

That seems to be in tune with the guidance Ford of England imparted in the owner’s manual for my Mk1 Cortina GT (great vehicle… thanks to Cosworth!): something like ‘for best fuel economy, shift at and cruise at the listed torque peak’. It always worked out that way for me, even with the GT’s engine, warmed-up quite a bit past the non-GT models (yet with less top-end than the Lotus-Cortinas). OTOH the GT manual also said that the best acceleration could be achieved by shifting 200-300rpm over the engine’s listed horsepower peak; also borne out many times, accompanied by predictably significant loss of fuel mileage, but an increase in smiles per gallon!

That still begs the question, of why an EFI couldn’t be programmed to run at least as lean as a carbed engine, under the conditions stated above. Aren’t the dry air runners of the EFI intake, plus the high pressure injectors, supporting a superior fuel atomization to a carbed intake’s flow?

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #6 by arse_sidewards » Tue Mar 11, 2014 10:10 pm

J.R. wrote:That still begs the question, of why an EFI couldn’t be programmed to run at least as lean as a carbed engine, under the conditions stated above. Aren’t the dry air runners of the EFI intake, plus the high pressure injectors, supporting a superior fuel atomization to a carbed intake’s flow?


An EFI can be programmed in that way. You wouldn't pass smog.

Don't like it, write your congressman
1994 F150 4x4 8ft, engine is basically stock.

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

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #7 by J.R. » Tue Mar 11, 2014 10:55 pm

arse_sidewards wrote:
J.R. wrote:That still begs the question, of why an EFI couldn’t be programmed to run at least as lean as a carbed engine, under the conditions stated above. Aren’t the dry air runners of the EFI intake, plus the high pressure injectors, supporting a superior fuel atomization to a carbed intake’s flow?


An EFI can be programmed in that way. You wouldn't pass smog.

Don't like it, write your congressman


My 1960 truck has no emissions requirements, so... is a Megasquirt system sophisticated enough to be programmed to run the EFI as 'lean-while-in-light-load' conditions, yet at stoich or above with heavier demands for power?

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #8 by motzingg » Wed Mar 12, 2014 5:52 pm

first of all, mmmmmmhmmm cortina! i love those little guys... so so cool. the lotus ones especially...

as to the megasquirt, yea definitely, you can make it as sophisticated as you can write your code.

you could write an add-on code that would go into lean mode under certain conditions (if you're good at programming) or you could just leave certain areas in your fuel table run lean. once you get into it, its very easy to see how the computer uses sensor values to calculate fuel delivery using the tables, and you'll see pretty quickly where you can lean the tables out, just be careful because its a quick way to put a hole in your piston.

if you are using it for spark control, you can probably get things dialed in very lean by pulling timing to keep from burning out your piston.

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #9 by blmhawkeye » Wed Mar 12, 2014 8:57 pm

1969 f100 shortbed, c4 trani,240 inline, 3.00 9 inch, 215/75/15, petronix ignition in LOM Dizzy, comp cam 252, stock intake exhaust, autolite 1bbl

24.6 mpg at 2100 rpms and 15 inches of vacuum

Installed DUI unit to replace the LOM and there is a large difference driving it on freeway. will have new recording next month when I do my round trip to tuscon from phoenix
Last edited by blmhawkeye on Wed Mar 12, 2014 8:59 pm, edited 1 time in total.

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #10 by THE FRENCHTOWN FLYER » Wed Mar 12, 2014 8:57 pm

motzingg wrote:...if you are using it for spark control, you can probably get things dialed in very lean by pulling timing to keep from burning out your piston.



...but that may also melt the heads of the exhaust valves off.
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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #11 by nightwatchman59 » Wed Mar 19, 2014 1:56 pm

Your gas mileage depends on a lot of things. Best ever gas mileage I got w/ a 3oo Ford six was in a brand new 1985 base model F-150, no factory a/c with overdrive 4 spd manual trans. I commuted from Front Royal, Va. 80 miles to Washington D.C. five days a week, in "pre rush hour traffic".
I averaged 24-25 mpg. the only change was 255/70/15 tires on the rear, 235/75/15's on the front, when the original tires were replaced at about 25k.
I do the speed limit... and that means stay to the right during rush hour... but I'll go w/ the flow in the middle lanes as required.
I granny shift, and shift into the next gear as soon as the engine can work with it.
I believe 300's are at their best at 1800-2000 rpm. When I wanted gas mileage I put 247k miles on a '94 FESTIVA.
THAT was a thrill ride you won't find at SIX FLAGS. :nod:

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #12 by arse_sidewards » Wed Mar 19, 2014 6:23 pm

nightwatchman59 wrote:When I wanted gas mileage I put 247k miles on a '94 FESTIVA.
THAT was a thrill ride you won't find at SIX FLAGS.

The thrill entirely depends how long it took you to put those 247k on it.

I once averaged 85ish mph over a 5k oil change (not in my truck).
1994 F150 4x4 8ft, engine is basically stock.

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

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #13 by 1986F150six » Thu Mar 20, 2014 8:12 am

arse_sidewards wrote:
nightwatchman59 wrote:When I wanted gas mileage I put 247k miles on a '94 FESTIVA.
THAT was a thrill ride you won't find at SIX FLAGS.

The thrill entirely depends how long it took you to put those 247k on it.

I once averaged 85ish mph over a 5k oil change (not in my truck).[/
quote]

And, your 5000 mile oil change interval lasted 58.8 hours of driving!!! :) WOW!

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #14 by MechRick » Thu Mar 20, 2014 10:16 am

J.R. wrote: is a Megasquirt system sophisticated enough to be programmed to run the EFI as 'lean-while-in-light-load' conditions, yet at stoich or above with heavier demands for power?


Easy. Just use a wideband and set the high manifold kph bins to use target tables to whatever fuel ratio you want. My last one hunted for 15.5-15.8 at light throttle cruise.

The problem is leftover oxygen allowing combustion on the exhaust stroke. Therefore, if you try that at high loads you will eventually melt a piston or valve. An essential tool for such experiments would be an egt on the warmest (leanest) cylinder. In fact, with Megasquirt it would be pretty easy to use egt as a fuel ratio modifier to prevent meltdowns...

At a certain lean point combustion would start to suffer and efficiency would drop. That point varies widely dependent on ambient air temperature, engine temperature, fuel quality, etc...this is where it is best to abandon homogenous combustion and go to stratified (not completely mixed) charges. Honda had great success at 18:1 with their stratified charge engines...
1994 F150, 4.9L/ZF 5 speed, C-Vic police driveshaft
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Stock cam, aluminum cam gear
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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #15 by Soldmy66 » Thu Mar 20, 2014 12:07 pm

Some of you might want to take a look at Ecomodder(dot)com.

There is a tremendous amount of minimum mileage based information on that forum.

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #16 by arse_sidewards » Thu Mar 20, 2014 10:52 pm

1986F150six wrote:
arse_sidewards wrote:
nightwatchman59 wrote:When I wanted gas mileage I put 247k miles on a '94 FESTIVA.
THAT was a thrill ride you won't find at SIX FLAGS.

The thrill entirely depends how long it took you to put those 247k on it.

I once averaged 85ish mph over a 5k oil change (not in my truck).[/
quote]

And, your 5000 mile oil change interval lasted 58.8 hours of driving!!! :) WOW!


1-4 highway hours per trip, used on weekends only, most weekends for a little more than two months.

Probably a lot longer than 60hr if you count time I spent idling.
1994 F150 4x4 8ft, engine is basically stock.

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

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #17 by blmhawkeye » Fri Apr 04, 2014 3:32 pm

Did my drive to tuscon, only problem is that I drove 70 down in back as I had a bit of an emergency to take care of. however, instead of the normal 15mpg I get I got 16.5 mpg

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #18 by mutt » Sat Apr 05, 2014 10:22 am

damn, you pickup chaps get some great mileage. An Econoline MPG just drops off a cliff above 60MPH.
When I first got my ekonokrate it was box stock- 4sp/OD, 3.08 rear. Didn't have the power to pull OD (good compression, sound engine) got 13-14 MPG.
I then, over time, did most of the hop ups folks use here. A big 2150 2bbl, Offy, port matched, intake bowl work, FI ex. manifold, Chev rockers, FI type plugs. Cam "straight up". I ran a big vac gauge, and tach. One thing I kept doing was dropping the power valves opening inHg, now I have a 2. Thats because manifold vacuum drops very often in everyday driving, dumping fuel thats really not needed in the application. But OD was problematic because to be able to use it, I gotta run the truck above its "critical mach" as far as wind resistance/mpg goes, so I put in a 3.80 rear and got better MPG, actually, as it optimized the rpms to my target MPH- 55, 60.
ANYWAY , keeping my foot out of it, I can get 19-20 MPG (corrected speedo) loaded with 2 harleys, one on a trailer. Id love to see 23 mpg.
I run 55 psi skinny light truck tires, too. Gutted cat into a cherry bomb. Stock ignition.
Next thing would be getting the compression up to 8.75, 9 tops. Thats what it really wants. No cheap way to do it, as of yet. Id like to see a dished piston as in stock, with the dish filled in where the flat part of the combustion chubbier is.... that would give some squish, Im thinking.

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #19 by arse_sidewards » Sat Apr 05, 2014 11:29 pm

blmhawkeye wrote:Did my drive to tuscon, only problem is that I drove 70 down in back as I had a bit of an emergency to take care of. however, instead of the normal 15mpg I get I got 16.5 mpg


Odd stuff happens with our trucks at highway speed.

I once got 18.x mpg at 65-85mph but that was literally getting onto the highway with two full tanks of fuel and getting off with less than 1/4 in the rear tank. It was also a 2AM-8AM drive so there was literally no traffic. I got 14.x on the way back because I drove at WOT because I was tired and wanted to get home before I fell asleep. This was back when I had a front air dam and hubs that actually unlocked.

I suspect it has something to do with aerodynamics going off a cliff sometime after 50mph but not degrading much more after that. With OD our truck also tend to be geared so the entire top third of the speedo is in the 300's efficiency sweet spot (1500rpm at 60mph) and the throttle is usually close to WOT at anything above 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: MPG experiment...[4.9L/300 engine prefers low revs] - UP

Post #20 by 1986F150six » Mon Apr 07, 2014 3:30 pm

The weather is moderating and I always notice improved mileage with warmer temperatures. [less choke usage and switch from winter blend gasoline?]

Here are some updated figures. Sometimes, I dream of "hopping up" the engine, but when I am reminded of how well this combination actually performs [efficiency wise], I say to myself, "Are you crazy; why mess with a good thing?" :mrgreen:

By the way, for those who might want to duplicate for mileage, the engine timing was set by vacuum gauge. At ~750 RPMs, the engine can pull 22" of Hg, but is set to ~19.75". The distributor is a recurved Duraspark with a MSD 6A box operating as a stand alone [no Duraspark ignition module]. Some might suggest having the idle speed lower, but 750 RPMs works well regarding A/C usage and alternator output when under an electrical load. It does not "run on" when the engine is cut off.

3/3/14 cool 16.95 mpg

3/11/14 mild 18.63 mpg

3/18/14 cool 16.91 mpg

3/25/14 cool/mild 18.69 mpg

4/3/14 warm 18.52 mpg

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Re: MPG experiment... [4.9L/300 engine prefers low revs]

Post #21 by arse_sidewards » Thu Apr 10, 2014 10:41 pm

I just filled up, got 14mpg, all with hubs locked (lifted 3" and missing air dam). I just swapped to a 2" larger water pump pulley (I was using a pulley from a van, swapped back to my stock truck pulley) yesterday so we'll see if that makes a noticeable difference.
1994 F150 4x4 8ft, engine is basically stock.

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

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