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EFI vs Carb Fuel Economy for the big six ...

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lasitter
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EFI vs Carb Fuel Economy for the big six ...

Post #1 by lasitter » Fri Feb 26, 2010 2:21 am

Which does better, and what scenarios might influence the outcome?

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Re: EFI vs Carb Fuel Economy for the big six ...

Post #2 by Lazy JW » Fri Feb 26, 2010 9:16 am

Well............ that depends :D

Speaking in VERY general terms, it is pretty tough to beat the EFI engines for consistent fuel milage, but the very best economy reported here on Fordsix comes from carbs. Specifically, mid 1980's F-150's with feedback carb, tall gears and overdrive four-speeds driven by Grandpa.

Still tough to beat the EFI rigs.
Joe
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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Re: EFI vs Carb Fuel Economy for the big six ...

Post #3 by StrangeRanger » Fri Feb 26, 2010 11:05 am

Again as a generalization. If you have one specific set of operating conditions (like 65 MPH on flat roads pulling a known trailer weight), you can tune a carb system for that set of conditions and beat the pee out of EFI for mileage as long as you operate in that set but you will lose badly everywhere else. If you have a variety of conditions like most of us do, EFI will generally win out for mileage and produce a wider range of performance while doing so.
1996 F-150 (tow missile)
1993 Mustang 5.0 (hot rod and auto-x monster)
1982 Tiga Formula Ford (SCCA racecar)
2013 Hyundai Elantra Coupe (daily driver)

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Re: EFI vs Carb Fuel Economy for the big six ...

Post #4 by 80broncoman » Fri Feb 26, 2010 11:16 am

Agree with SR And as allways the driver his/her driving style has more input then anything else.
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Re: EFI vs Carb Fuel Economy for the big six ...

Post #5 by THE FRENCHTOWN FLYER » Fri Feb 26, 2010 11:57 am

Lazy JW wrote:Well............ that depends :D

Speaking in VERY general terms, it is pretty tough to beat the EFI engines for consistent fuel milage, but the very best economy reported here on Fordsix comes from carbs. Specifically, mid 1980's F-150's with feedback carb, tall gears and overdrive four-speeds driven by Grandpa.

Joe


That was my experience with an '85 Econoline w/ manual OD: 21+ mpg @ 55 mph steady state.
But I would trade it for a 5-speed EFI in a heartbeat.
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

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Re: EFI vs Carb Fuel Economy for the big six ...

Post #6 by tom954x4 » Fri Feb 26, 2010 3:20 pm

Mutt's posts talk about staying out of the power valve triggered by low vacuum to get better mileage.

In an EFI, is there a similar phenomenon, or is fuel delivery a linear function of thottle and vacuum (other factors being equal)?

Another Q: in an EFI with manual tranny, if you coast in gear does the PCM deliver minimal or no fuel to the engine? In my diesel DD, no fuel is delivered in this scenario with engine above about 1200 rpm.
1995 F-150 XL, 300-6, 4x4, ex-cab, sb, 3.08 5-speed, 2 1/2 in. exhaust w/flowmaster 50, MSDignition failed with no warning, now out, canopy, 179,000 + miles. Gone but not forgotten 1965 F-100 240 3spd lwb "the green hornet"; 1960 F-250 4x4, 223 six, 4sp with wrap-around rear window, two-tone paint, overhead camper.
Tow vehicle: 2012 F-250 4x4 6.7 diesel XLT s/c lwb

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Re: EFI vs Carb Fuel Economy for the big six ...

Post #7 by StrangeRanger » Fri Feb 26, 2010 3:55 pm

EFI keeps the air/fuel ratio at a stoichiometric 14.7:1 whenever you are in "warm cruise" mode. When the Throttle Position Sensor registers WOT (wide Open Throttle) it richens to somewhere around 12.5-13.0 but as long as the ECT (Engine Coolant Temperature) sensor says the engine is at or near operating temperature the PCM will maintain 14.7 at all throttle positions from idle to just under WOT.
1996 F-150 (tow missile)
1993 Mustang 5.0 (hot rod and auto-x monster)
1982 Tiga Formula Ford (SCCA racecar)
2013 Hyundai Elantra Coupe (daily driver)

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tom954x4
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Re: EFI vs Carb Fuel Economy for the big six ...

Post #8 by tom954x4 » Fri Feb 26, 2010 5:33 pm

Thank you SR. The operation of EFI per your explanation would seem to be the basis for your general observation that "in a variety of conditions like most of us do, EFI will generally win out for mileage and produce a wider range of performance while doing so".

It would also explain that if you have an air leak in the intake the PCM compensates by dumping in more fuel to main the Stoich ratio causing faster idle and a drop in city mpg in an EFI. (a problem I am still working on now in and subject of a recent post), :bang:

I am still learning, but good stuff. :thumbup: :thumbup:
1995 F-150 XL, 300-6, 4x4, ex-cab, sb, 3.08 5-speed, 2 1/2 in. exhaust w/flowmaster 50, MSDignition failed with no warning, now out, canopy, 179,000 + miles. Gone but not forgotten 1965 F-100 240 3spd lwb "the green hornet"; 1960 F-250 4x4, 223 six, 4sp with wrap-around rear window, two-tone paint, overhead camper.
Tow vehicle: 2012 F-250 4x4 6.7 diesel XLT s/c lwb

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Re: EFI vs Carb Fuel Economy for the big six ...

Post #9 by Lazy JW » Fri Feb 26, 2010 8:36 pm

StrangeRanger wrote:EFI keeps the air/fuel ratio at a stoichiometric 14.7:1 whenever you are in "warm cruise" mode......


Yup. And this is exactly why it is possible to sometimes get better fuel economy with a carb; the carb "may" be tuned to run leaner, whereas the EFI wants to stay right at stoich.

Getting a carb to run consistently leaner while still performing well AND maintaining allowable emissions is a tall, tall order. That's why the car makers, with all of their R&D money, opted for EFI. It isn't likely that this old hillbilly could pull it off either.
Joe
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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Re: EFI vs Carb Fuel Economy for the big six ...

Post #10 by rikard » Sat Feb 27, 2010 5:01 pm

JW & SR are right on (as usual).
I have a vacuum gauge on my 95 EFI 300 which I use mostly as a early warning device and as a "load meter" . When I had the gauge on my carbed vehicles I would keep it out of the power valve area to increase gas mileage. My vacuum gauge has been on six vehicles. With my current ride on a level road with no wind I can maintain 10" at 70 mph. If I reduce my speed to 60 it will hold about 12". I can feel a difference when it drops below 4".
My truck will net about 20 mpg at 60 mph and 18 at 70. 95 2x4 F150 300 5 speed 3.08 gears. 235/75/15 tires.
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rikard
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Re: EFI vs Carb Fuel Economy for the big six ...

Post #11 by ClayPigeonKiller » Tue Mar 02, 2010 3:10 pm

21mpg with efi. I think a carbed truck could do the same thing. For a daily driver i would suggest injection. I have both and even with the carbed stuff on the numbers efi is still easier to use in cold starts and heartless miles encountered in the daily grind.

Adam
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1964 Ford Galaxe- 435, 4 speed
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Re: EFI vs Carb Fuel Economy for the big six ...

Post #12 by IllSHOyou » Tue Mar 02, 2010 4:40 pm

Mine is getting high teens. 2.73 Rear 2000 rpm @ 80 MPH 5 Gear

While the other trucks may net better mpg in the 60-70 MPH range with 3.08 gears. Mine does great for the speed demon.

I think I am between 16-18 MPG right now at 80 MPH.

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Re: EFI vs Carb Fuel Economy for the big six ...

Post #13 by IllSHOyou » Tue Mar 02, 2010 4:42 pm

IllSHOyou wrote:Mine is getting high teens. 2.73 Rear 2000 rpm @ 80 MPH 5 Gear

While the other trucks may net better mpg in the 60-70 MPH range with 3.08 gears. Mine does great for the speed demon.

I think I am between 16-18 MPG right now at 80 MPH.


Unfortunately, I am having issues with the fuel tanks transferring fuel, So I cant give a hard number at this time, but its pretty good.

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Re: EFI vs Carb Fuel Economy for the big six ...

Post #14 by lasitter » Tue Mar 02, 2010 7:27 pm

IllSHOyou wrote:I think I am between 16-18 MPG right now at 80 MPH.
I have the same rear end, and I think this is outstanding economy considering the drag coefficient of the truck was never designed for economy at this speed.

Do you have a tonneau, or just an open bed?

Many thanks to everyone that has replied to this thread. It has been very enlightening.

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Re: EFI vs Carb Fuel Economy for the big six ...

Post #15 by tom954x4 » Tue Mar 02, 2010 8:00 pm

my numbers are the same as rikard, above, with a 4X4, '95, bone stock, see signature for details. Note- I have a shell. See the eye candy department for some pics on photobucket. 99 per cent of my "highway" driving is on rural roads at 50 to 55 and I am right at the cusp between 4th and 5th, not sure which is better on the flats.

I may be going on a long trip to Oregon over 55 mph roads in April, 260 miles each way, and am planning on an experiment - drive down on 5th and back in 4th over the exact same route. Maybe a difference will show up. At a steady 50 to 55, no wind, flat, I am probably steady state 20-21 but too many starts and stops on my regular use of the truck to average close to that tank to tank. 20 or maybe 21 tops is asymptote value for mileage with my rig, so it seems. Not bad, I say. Driving habits are critical, as noted by 80broncoman at the top of the thread.
1995 F-150 XL, 300-6, 4x4, ex-cab, sb, 3.08 5-speed, 2 1/2 in. exhaust w/flowmaster 50, MSDignition failed with no warning, now out, canopy, 179,000 + miles. Gone but not forgotten 1965 F-100 240 3spd lwb "the green hornet"; 1960 F-250 4x4, 223 six, 4sp with wrap-around rear window, two-tone paint, overhead camper.
Tow vehicle: 2012 F-250 4x4 6.7 diesel XLT s/c lwb

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Re: EFI vs Carb Fuel Economy for the big six ...

Post #16 by StrangeRanger » Tue Mar 02, 2010 8:14 pm

With 3.08 gears and stock tires you're at about 1630 RPM @ 55 MPH in 5th and about 2040 in 4th. I'd guess that on a dead flat road 5th might work better but maybe not. I think that your revs are just a skosh too low for max economy and that 2040 may be a skosh too high. You're probably right that it's a push. Take it up to 60 and 5th gear (1780 RPM) should win out all the way.
1996 F-150 (tow missile)
1993 Mustang 5.0 (hot rod and auto-x monster)
1982 Tiga Formula Ford (SCCA racecar)
2013 Hyundai Elantra Coupe (daily driver)

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tom954x4
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Re: EFI vs Carb Fuel Economy for the big six ...

Post #17 by tom954x4 » Wed Mar 03, 2010 12:58 pm

SR, your comments agree precisely with my own thinking and the way the truck feels.

Over the last 33 years I have driven a variety of carbed and EFI Ford trucks and vans over 300,000 miles and they all basically got the same mileage, 13-15 in town and 18-20 on the highway under normal conditions and resonable speed < 70 mph.

'65 F-100, aka The Green Hornet (carbed 240, no OD)
'66 Bronco with carbed 289 v8, 3 on tree
91 F-150 EFI 5 sp.
93 E-150 Van ("the lux mobile") with 3.55, AOD and 302 V8
current rig ('95)
The only exception was pop's '60 F-250 4x4 with a humongous overhead camper and the 223 six :shock: That thing took the family from WA to Massachusetts and everywhere in between. 11-13 mpg consistently. 60 mph top speed. On any mountain grade, took its own sweet time in the slow lane in 3rd at 30 mph. Bullit proof engine if there ever was one.
By the way, and off topic here, none of the carbed vehicles ever had an icing problem, all were bone stock, and I never even attempted to tune the carb either. :oops: :oops: I was too young to understand the contraption.
1995 F-150 XL, 300-6, 4x4, ex-cab, sb, 3.08 5-speed, 2 1/2 in. exhaust w/flowmaster 50, MSDignition failed with no warning, now out, canopy, 179,000 + miles. Gone but not forgotten 1965 F-100 240 3spd lwb "the green hornet"; 1960 F-250 4x4, 223 six, 4sp with wrap-around rear window, two-tone paint, overhead camper.
Tow vehicle: 2012 F-250 4x4 6.7 diesel XLT s/c lwb

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THE FRENCHTOWN FLYER
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Re: EFI vs Carb Fuel Economy for the big six ...

Post #18 by THE FRENCHTOWN FLYER » Wed Mar 03, 2010 3:06 pm

tom954x4 wrote:I may be going on a long trip to Oregon over 55 mph roads in April, 260 miles each way, and am planning on an experiment - drive down on 5th and back in 4th over the exact same route.

I would drive halfway there in 4th and halfway in 5th, then do the same on the way home to try to minimize external factors. Of course you would need to stop midway to refuel and note mileage.
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Re: EFI vs Carb Fuel Economy for the big six ...

Post #19 by IllSHOyou » Wed Mar 03, 2010 4:00 pm

lasitter wrote:
IllSHOyou wrote:I think I am between 16-18 MPG right now at 80 MPH.
I have the same rear end, and I think this is outstanding economy considering the drag coefficient of the truck was never designed for economy at this speed.

Do you have a tonneau, or just an open bed?

Many thanks to everyone that has replied to this thread. It has been very enlightening.


No tonneau cover, 2WD and a Tool Box.

I think the performance would be even better with the cover. I just performed all the maintenance recently too: Belt/Cap/Rotor/OEM Plugs/Spark Plugs

I think the engine likes at least 1800 rpm. Its hard to sustain less than 1800 rpm on the highway in fifth gear. No chance on a hill. If I were a economy guy I would put a little shorter gear in the rear end and run about 60 MPH.

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Re: EFI vs Carb Fuel Economy for the big six ...

Post #20 by StrangeRanger » Wed Mar 03, 2010 4:08 pm

I know anecdotal evidence is always suspect but...the highest mileage claims seem consistently to come from trucks with a 5 speed and 3.27/3.31 gears (1900 RPM @ 60) or a 4 speed and 2.73 gears (1970 RPM @ 60)
1996 F-150 (tow missile)
1993 Mustang 5.0 (hot rod and auto-x monster)
1982 Tiga Formula Ford (SCCA racecar)
2013 Hyundai Elantra Coupe (daily driver)

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Re: EFI vs Carb Fuel Economy for the big six ...

Post #21 by mutt » Fri Mar 05, 2010 2:37 pm

too far down in the torque curve for me. I think Ill finally be able to put in a 3.71 rear on the Ekonokrate.
the 4sp OD (80, iron case) has a wacking great gulf between 2nd & 3rd. This is a real PITA loaded in the mountains...wont hold 3rd, second screams @ 47mph. The beast is just turning too slow @60 in 3rd/OD, - and pushing all that air! to be efficient. If i swap out the gears- or, rather: $180 installed, new axle bngs., the coming run up to Montana will show if a taller numerical rear end will result, as I think, in better MPG.
Other than THAT, the rugged old beast is as dependable as the dawn. theres nuthin to tinker. I open the "hood" & look at it, but it dosnt require anything from me but oil.
The 2150 is providing a jot more mpg, and smoother idle, but the 2100's throttle shaft was loose as a goose.
The roll on hunter green/black rustoleum paint job makes the old boy look quite .....jaunty, in a dissollute mercenary sort of way.......

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