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Why do carbs seem to do better than EFI for MPGS on 300s?

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Pathines
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Re: Why do carbs seem to do better than EFI for MPGS on 300s?

Post #51 by Pathines » Thu Aug 22, 2019 3:19 pm

xctasy wrote:Welcome Pathines!

Notible examples of great carb engines verses Bosch injection are the triple Weber Maserati Meraks, 8bbl Aston Martins, triple Weber DB6 and DBS Vantages in the 68 to 72 era where EFi or MFi got withdrawn due to service requirements.


Now, now, you've thrown in extremely expensive carbs versus near stock FI.
Image

You'd have to find a mechanic that knows how to tune the multiple circuits one finds on a Weber carb. Back in the day, there was a company that made manifolds for the Corvair flat six to take two triple-barrel downdraft Webers. You machined off the cast in factory manifold, drilled and tapped a few bolt holes, attached the new manifolds, and installed and tuned the new Webers. Very expensive, but it put out over 200 hp from 164 cubic inches. I had a '65 Corvair with the 140 horse engine with four one barrel carbs. It ran well as long as the carbs were synched.

I did figure out how to re-jet the carbs on my 1986 Yamaha FZ750, which didn't run well at low speeds around town because in its California set up it was extremely lean. Changing the idle jets and the main jets cured all of that and the engine ran much cooler too, with slightly better MPG.

Back to today, I don't think a carbed 4.9l will get better MPG than a EFI 4.9l, both in good fettle.
'93 F-150, 4.9L, 5-speed, stock, lots of miles

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Re: Why do carbs seem to do better than EFI for MPGS on 300s?

Post #52 by xctasy » Thu Aug 22, 2019 3:34 pm

With respect, Wrong, even a 1bbl modified 67 200 can make over 105 rwhp, and Ak Miller used this kind of process to get 35.6 US Mpg out of a 1-bbl 1967 200 Mustang in the MobilGas Total Economy run. 55mph average.

The accounts of others here are true. Both 1bbls and EFi get great mileage. Lasitters F150 gets IIRC, 32 to 35 mpg. The LazyJW White Ox can do 19.

Back to back, a 2-bbl in line six will exceed the fuel economy and power of a port injected sequential or batch fire EFi, because those systems operate on Government mandated 14.7 or 15.15:1 stoich ratios in closed loop, and that is a 10% loss according to Renault in 1982.

My Morse tests on air fuel using six 02 sensors on a 1-bbl six cylinder engine shows the same thing.


Fords EFi engines of the 1985-1986-1987 era had worse mpg than the carb versions, with a modest performance increase that was always hooked into open and closed loop control.

I've logged mpg, everything from OBDII port on my 98 Explorer, and same thing. So I can make almost any carb engine do better mpg while maintining the same speed just by opting out of stoich. Ford engineers did this, then had to relent. The non feedback carb engines ran leaner than the feedback YFA F150 trucks.


The whole mpg verses MPH thing was worked out by the Snook formula used in LeMans Index of Efficency trials. The French and Italians nutted it out back in the late 50's. The independnt runner thing, well, that's always been a non starter for US guys. Its not expense. Ford did it with the dual inline Autolite four barrels on 302's and 429's back in 1970, then they had to sell off Autolite....

IR/ITB tuning, the Italians and English mastered that, and then went Injection. The EFi engines then got there clean cat claws clipped by stoichometric closed loop requirments, technically to suit catalyst life.
Last edited by xctasy on Thu Aug 22, 2019 4:12 pm, edited 1 time in total.
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Pathines
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Re: Why do carbs seem to do better than EFI for MPGS on 300s?

Post #53 by Pathines » Thu Aug 22, 2019 3:49 pm

xctasy wrote:Wrong, even a 1bbl modified 67 200 can make over 105 rwhp, and Ak Miller used this kind of process to get 35.6 US Mpg out of a 1-bbl 1967 200 Mustang in the MobilGas Total Economy run.

The accounts of others here are true. Both 1bbls and EFi get great mileage. Lasitters F150 gets 35 mpg. The LazyJW White Ox can do 19.


My younger brother had a 1966 Mustang with the small six in it, pretty lame powerwise. On the other hand, I had a 1979 Mustang with a 5l engine, sucking through a Ford two barrel carb, with that weird four speed overdrive transmission. It was lame, too. Then I made some upgrades, new Comp Cams 268, new lifters for the cam, Edelbrock high rise manifold, and a Carter AFB carb. Those mods woke it up big time, when I added a full dual exhaust, H pipe, and Turbo mufflers, it overpowered the suspension which remained stock. Fun to drive and had a great idle sound.

Still, I'm comparing carbed 4.9l to EFI 4.9l. I'd love to see those two engines on a rolling dynomometer.
'93 F-150, 4.9L, 5-speed, stock, lots of miles

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Re: Why do carbs seem to do better than EFI for MPGS on 300s?

Post #54 by pmuller9 » Thu Aug 22, 2019 3:58 pm

Pathines wrote:Still, I'm comparing carbed 4.9l to EFI 4.9l. I'd love to see those two engines on a rolling dynomometer.

Totally stock comparison or does a person get to do some tuning.
The carburetor 300 had different compression ratios from very low to low where the EFI 4.9 were mostly 8.8:1

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Pathines
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Re: Why do carbs seem to do better than EFI for MPGS on 300s?

Post #55 by Pathines » Thu Aug 22, 2019 4:10 pm

pmuller9 wrote:
Pathines wrote:Still, I'm comparing carbed 4.9l to EFI 4.9l. I'd love to see those two engines on a rolling dynomometer.

Totally stock comparison or does a person get to do some tuning.
The carburetor 300 had different compression ratios from very low to low where the EFI 4.9 were mostly 8.8:1


Yes, I've read about the different compression ratios. I'd "permit" tuning the engines as long as you're limited to a screwdriver, pair of pliers, and for me, a voltmeter. :D

I have some old BMWs with FI, in fact, all of them have some sort of FI, even my 1972 CSi with its primitive D-Jetronic system. I used to have a running joke with a friend who had a carb equipped CS. I'd tell him that the hissing noise his car made at idle was the air fighting its way through the carb, while my EFI car, identical otherwise, was much quieter because those beautiful FI tubes didn't fight the air.

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'93 F-150, 4.9L, 5-speed, stock, lots of miles

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Re: Why do carbs seem to do better than EFI for MPGS on 300s?

Post #56 by bubba22349 » Thu Aug 22, 2019 7:50 pm

pmuller9 wrote:
Pathines wrote:Still, I'm comparing carbed 4.9l to EFI 4.9l. I'd love to see those two engines on a rolling dynomometer.

Totally stock comparison or does a person get to do some tuning.
The carburetor 300 had different compression ratios from very low to low where the EFI 4.9 were mostly 8.8:1


In my OPIN a fair comparison for the Carbed vs EFI shootout test would be a stock spec pickup 300 short block (1965 to 1985) a 240 head or milled 300 head to get a 8.8 to 1 compression ratio with stock size valves, a stock DuraSpark II Ignistion system, and a 1968 Autolite or later Carter YF carb up to the last feedback version along if its used with its stock TFI Ignition. :thumbup: :nod:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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Re: Why do carbs seem to do better than EFI for MPGS on 300s?

Post #57 by sdiesel » Thu Aug 22, 2019 8:51 pm

I do like what mech rick has to say about building EFI, out of found parts.

it reality now.
Egr or no, it's the hot rodders of today

I could literally put one together from my parts pile...in a weekend of steady work
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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