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

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

Post #1 by argo » Wed Jul 24, 2013 12:13 am

I have never understood why EFI is less fuel efficient on these engines than a carb setup. It baffles me because it seems to be an anomaly. EFI tends to be more efficient on almost any other type of engine. Does it maybe have something to do with the cam timing more so than the fuel delivery?
"The Argo" 321,000 miles and counting
It was a 1996 2wd Ford F-150 300ci Inline 6 NP-435 2.73:1 8.8" Rear;
It is a 1996 4wd Ford F-150 300ci Inline 6, C6 Transmission, 3.55:1 axles (limited slip in rear), BW 1356 manual shift transfer case with manual hubs
"Ah Ha Ha Ha Ha Ha! I Swear! Tractors is so dumb!" - Mater

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

Post #2 by Asa » Wed Jul 24, 2013 9:13 am

It depends on your definition of "efficient"

Carbs can be tuned so that at a certain RPM, they run just a little bit lean and they use less fuel. EFI is setup so that it always provides the optimal A/F ratio. Because of this EFI gives the better power because it is more often at the optimal A/F ratio while carbs can give better MPG.

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

Post #3 by argo » Wed Jul 24, 2013 10:51 am

Yes... and no. It seems plausible and I am sure that a careful tuner could get a carb to be more efficient... untill barometric pressure changes, temperature changes, etc. The other issue I have with that idea is that it seems to be nearly exclusively confined to this engine family. That is why I am conjecturing about the cam timing issue. What year did Ford retard the cam timing on the 300? Also, since most people will replace their timing set on their carbureted engines with one that installs the cam "straight up" even later carbureted engines which originally had retarded cam timing will effectually be set to 0* upon timing gear replacement, engine freshening, or a rebuild. I don't know if the same holds true for an EFI engine. If the EFI engine were to have it's cam installed "straight up" would the EFI have problems? If not, would the EFI engine be able to lay down some more impressive MPGs?
"The Argo" 321,000 miles and counting
It was a 1996 2wd Ford F-150 300ci Inline 6 NP-435 2.73:1 8.8" Rear;
It is a 1996 4wd Ford F-150 300ci Inline 6, C6 Transmission, 3.55:1 axles (limited slip in rear), BW 1356 manual shift transfer case with manual hubs
"Ah Ha Ha Ha Ha Ha! I Swear! Tractors is so dumb!" - Mater

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

Post #4 by ludwig » Wed Jul 24, 2013 11:56 am

My first F150 1986 model had the 302 and the first generation of throttle body EFI. They sold it as being more fuel efficient and whatever. After the break in period (50k or was it 75k?), the fuel efficiency was never particularly spectacular. Then I I had a couple repairs.

They told me that the EFI was not a fuel efficiency enhancer. It gave quicker, more dependable starts and reliable ignition. Period. Something about manifold FI vs. cylinder FI or some such. I'm still not convinced that it was much of an improvement.

And my current 1995 F150 with the I6 and EFI barely gets in the 18 mpg range. Usually it is in the mid 17s. But hey, it's got killer torque.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #5 by THE FRENCHTOWN FLYER » Wed Jul 24, 2013 3:34 pm

Short answer: EFI engines have to cruise at an A/F ratio near to 14.6:1 so the EGO sensor will function. Carbs can have an A/F ratio above 15:1 at cruise mode so they will possibly get better highway fuel economy, even though the throttling processes associated with a carb venturi will increase pumping losses.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #6 by ludwig » Wed Jul 24, 2013 4:48 pm

Interesting. Now I know. Thanks.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #7 by argo » Wed Jul 24, 2013 11:28 pm

Emissions are a big part of it. Particularly the emissions of NOx, because lean mixtures cause higher combustion temperatures. Nitrogen is an inert gas until combustion temperature exceeds 2300 degrees. When the flame front exceeds that temperature, Nitrogen molecules (N2) separate into Nitrogen atoms, which the recombine with oxygen, creating compounds that ultimately become nitric acid, which forms acid rain. EGR reduces the combustion temperature by partially filling the cylinder with an inert gas (exhaust) which slows the burn rate, and also absorbs heat, expanding as a result and assisting with pushing down the piston. A stoichiometric air fuel ratio burns cooler than a lean mixture (16:1 for example), which also helps keep combustion temperature below 2,300 degrees F. Reduced cylinder pressure (through lower compression and/or retarded cam timing) reduces combustion temperature as well.

With the feedback carbureted and EFI engines, we have all three elements in play. We have lower cylinder pressure (8.8:1 compression ratio and 4* retarded cam timing) we have a stoichiometric A/F ratio, and we have EGR. A carbureted engine might have a straight up cam, a higher compression ratio, and a leaner cruise mixture. The carbureted engine listed would have a much higher NOx emission profile, while the EFI system would be less fuel efficient but also pollute less. However, with a healthy catalyst and an increase in EGR, a leaner cruise A/F ratio and "straight up" cam would have a negligible impact on NOx from the tailpipe (it would be higher at the exhaust port) and improved fuel economy. The downside is it would make the engine more detonation prone, which could cause engine damage if driven by the average "gas and go" consumer. That is nothing new. Carbureted engines were always factory jetted to be slightly rich for less drivability issues and to preserver engine integrity. This is why re-jetting for better power often times required leaner jets back in the day, not richer.

This discussion is good. I am beginning to see the bigger picture, and perhaps how I can bump the cam timing to 0* and slightly lean my cruising A/F ratio and also modify the DPFE signal to get some more EGR flow to reduce NOx emissions and increase fuel economy at part throttle. Hmm. I can't wait until I am better so I can try it!
"The Argo" 321,000 miles and counting
It was a 1996 2wd Ford F-150 300ci Inline 6 NP-435 2.73:1 8.8" Rear;
It is a 1996 4wd Ford F-150 300ci Inline 6, C6 Transmission, 3.55:1 axles (limited slip in rear), BW 1356 manual shift transfer case with manual hubs
"Ah Ha Ha Ha Ha Ha! I Swear! Tractors is so dumb!" - Mater

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

Post #8 by MechRick » Wed Jul 24, 2013 11:34 pm

If you can keep a carbed engine cruising with high intake manifold vacuum in a reasonably lean state, they will return great fuel economy. EFI is better in every other scenario, though...

My best carbed fuel economy...19 mpg, 4wd longbed 300 six/T18 at 55 mph steady freeway driving.
Best EFI through the mountains of Colorado, 18 mpg, 55-65 mph loaded with 1k (level bed) lifted 4wd shortbed, 4.9L/M5OD.
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EFI head w/mild port work, 3 angle valve job
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #9 by argo » Wed Jul 24, 2013 11:51 pm

My best ever was 21 MPG with the NP-435 and 2.73 rear end gears, but that was as a 2wd. I typically was in the 19.5-20 MPG range at conservative highway speeds (I do 55 in 55 MPH zones and 60 in 65 MPH zones) I am still unsure of my current mileage because I have not driven any significant distance with the 4wd AOD conversion, now with 3.55 gears and 31" tires. I am so far off the range compared to my original setup that I have no reasonable point of reference to even conjecture about fuel economy right now. I know my cruising RPM is lower (3.55x.67= 2.38:1 final drive ratio, and then the 31" tires reduce my cruising RPM another 6.5%), but I am lugging around about 500 more pounds, and because the truck sits significantly higher (and no, I did not install a lift kit) it now has more aerodynamic drag. Further complicating the equation is me. I had gastric bypass surgery, and I have already dropped 30 lbs in 2 weeks, plus an additional 30 I lost pre-surgery. I stand to loose another 150-170 lbs, thereby negating about half the weight gain of the truck by doing the 4wd and AOD conversion. And the worst part is I am not allowed to do anything while I recover, so I think about it constantly and I am driving myself nuts thinking about it because I can't let go of a puzzle or problem once I wrap my mind around it.
"The Argo" 321,000 miles and counting
It was a 1996 2wd Ford F-150 300ci Inline 6 NP-435 2.73:1 8.8" Rear;
It is a 1996 4wd Ford F-150 300ci Inline 6, C6 Transmission, 3.55:1 axles (limited slip in rear), BW 1356 manual shift transfer case with manual hubs
"Ah Ha Ha Ha Ha Ha! I Swear! Tractors is so dumb!" - Mater

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

Post #10 by E4ODnut » Thu Jul 25, 2013 7:50 am

Argo,
I agree with TFF, it's all about emissions. It is my understanding that the combustion chamber design was changed as well to help accomplish this.

Because EFI allows you much finer control of A/F ratio and ignition timing, I suspect that an earlier model carbed 300, converted to programmable EFI could be made to get slightly better economy and performance than it could carburetted, but it would probably not pass emissions standards.

On a side note, exhaust temperature is maximum at stoichiometric Air/fuel ratio (~14.7:1 for gasoline) and decreases either side of it. I've read lots of documentation to support this and proved it myself by changing my A/F ratio under a steady load and observing my EGT.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #11 by argo » Thu Jul 25, 2013 9:50 am

EGT does not correspond to peak combustion temperatures. if the mixture is still burning as it exits the cylinder, you will have higher EGT. Whereas, if you have a hot, fast combustion in the cylinder, EGT will be lower because the mixture is done burning and the gasses will have cooled due to cylinder expansion by then. The richer the mixture the hotter peak combustion temps are. This is why lean mixtures can burn holes in pistons (especially on air cooled 2 strokes). Retarded ignition timing also causes higher EGT but lower combustion temperatures too, whereas advanced timing causes higher temps (even detonation) but cooler EGT.
"The Argo" 321,000 miles and counting
It was a 1996 2wd Ford F-150 300ci Inline 6 NP-435 2.73:1 8.8" Rear;
It is a 1996 4wd Ford F-150 300ci Inline 6, C6 Transmission, 3.55:1 axles (limited slip in rear), BW 1356 manual shift transfer case with manual hubs
"Ah Ha Ha Ha Ha Ha! I Swear! Tractors is so dumb!" - Mater

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

Post #12 by motzingg » Thu Jul 25, 2013 10:45 am

chemically, the highest temp (pressure) and maximum energy extraction happens at stoichiometric, but in engines the practical max. power point comes slightly rich of stoich, 14.5 ish, according to what i've discussed with engineers who design engines. chemically i'm not sure why that happens, but i've had a couple of the very top minds in IC engines tell me that. I think it has more to do with spreading out the burn into a slower and more productive explosion, rather than a fast short explosion that only heats the walls of the piston, cylinder, head.

One engineer i've talked to extensively works with lean-burn high efficiency industrial engines, run on natural gas. They run very cool and low on power at lean (20:1+) ratios, but deliver exceptional fuel economy. Spark timing has everything to do with it, the spark timing computer is extremely sophisticated, and the engine runs off a carbureator.

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

Post #13 by THE FRENCHTOWN FLYER » Thu Jul 25, 2013 1:24 pm

motzingg wrote:chemically, the highest temp (pressure) and maximum energy extraction happens at stoichiometric, but in engines the practical max. power point comes slightly rich of stoich, 14.5 ish, according to what i've discussed with engineers who design engines. chemically i'm not sure why that happens...


You have to introduce enough fuel so that every single atom of oxygen has a chance to combust with fuel. If an oxygen molecule is on one side of the chamber and the closest unburnt fuel molecule is on the other side of the chamber then that O2 molecule will go out the exhaust unburnt. So having a leetle extra fuel in there gives the best chance of complete combustion. But TOO MUCH fuel means the excess fuel will just carry away some of the combustion heat and rob power without producing any work. Greatly oversimplified but you get the jist of it.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #14 by motzingg » Thu Jul 25, 2013 3:59 pm

thats very interesting FTF... reminds me of what my thermo professor used to say 'The fuel burns the air'

so why does the slightly lean reaction in my two stroke cause it to over heat so quickly? some of the race engines i've worked with will come close to seizing if the bowl runs dry. they also produce a power surge as that happens.

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

Post #15 by Asa » Thu Jul 25, 2013 8:06 pm

motzingg wrote:thats very interesting FTF... reminds me of what my thermo professor used to say 'The fuel burns the air'

so why does the slightly lean reaction in my two stroke cause it to over heat so quickly? some of the race engines i've worked with will come close to seizing if the bowl runs dry. they also produce a power surge as that happens.

The both of you have sort of talked around why it would do that. Excess fuel slows down the burn, so it makes sense that a slight lack of fuel would do the opposite. You run anything lean and you're going to heat up the engine.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #16 by motzingg » Fri Jul 26, 2013 2:15 pm

oh yeah duh, i knew that... fuel requires more heat to combust than air does, less air means for a reaction that happens too fast.

the thing that is interesting is that when emissions engines are running lean, they have to advance the timing. hence the CARB version of the DS2 with electronic advance. I cant imagine those CARB engines were running extreme lean, more than likely just a tiny bit lean. So if the burn happens faster with lean, why does the CARB engine advance?

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

Post #17 by Seattle Smitty » Fri Jul 26, 2013 3:34 pm

What's this that Argo said back there about lean-burning holes in 2-stroke pistons; who ever heard of such a thing!!?

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

Post #18 by E4ODnut » Fri Jul 26, 2013 10:01 pm

I run my 300 at between 16:1 and 18:1 AFR at light to medium loads. Been doing it for over 100,000 KM. No engine problems so far.

Any information I have suggests best power is usually between ~12:1 and ~13:1 AFR. In my experience my 300 and 460 both seem to like ~13:1, the 351s seem to prefer~12.8:1.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #19 by BIG 6 farmer » Sat Jul 27, 2013 5:20 pm

Back in the day, about 1980 or so. Alot of guys with newish F150s 300 sixes. Claimed to pull 20-27 mpg, on a good Hyw. trip. But the speed limit was 55 still. When the EFI sixes came out, heard a lot of crabby 15-20 mpg stories. :bang: My theory is, it has to do with heat in the mixture some what. We all agree?,that Gasoline vaporizes better with heated air. The EFI 300 six draws cold air into a cool intake Manifold. When i say cold/cool, im comparing to V8 which runs a warmer to hot intake. Thinking some time(on a EFI 300) i would like to try ducting hot air off the Exhaust Manifolds, to the air intake :hmmm: To see if it would improve MPGs. :D Did that years back on a 4 cyl. 91 Ranger. Made the turd run much smoother, & got better mileage. The Factory had a little one ran to Air cleaner box. I pulled all the intake air off the Exhaust Manifold, it liked it alot. But it was winter/spring time here also.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #20 by ludwig » Sat Jul 27, 2013 8:09 pm

I thought cold air was more dense, that means it has more oxygen per unit and the engine likes cold fresh air. The first EFIs ran really hot. Maybe that's a part of it.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #21 by BIG 6 farmer » Sun Jul 28, 2013 12:07 am

Yes your right. But that only is good for maximum power(like on a Race Car). For best MPGs & smooth running, you need heated air to properly vaporize the Gasoline. Kind of a trade off, one or the other. Unless you go to the extremes like Smokey Yunick did with his Heat Engines :hmmm: Yes they did work.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #22 by argo » Sun Jul 28, 2013 12:01 pm

I am back! I changed my email address and was locked out for a few days. Good discussion. Especially about the relative heat level of the EFI V8 intakes Vs the inline 6 intakes.
"The Argo" 321,000 miles and counting
It was a 1996 2wd Ford F-150 300ci Inline 6 NP-435 2.73:1 8.8" Rear;
It is a 1996 4wd Ford F-150 300ci Inline 6, C6 Transmission, 3.55:1 axles (limited slip in rear), BW 1356 manual shift transfer case with manual hubs
"Ah Ha Ha Ha Ha Ha! I Swear! Tractors is so dumb!" - Mater

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

Post #23 by BIG 6 farmer » Sun Jul 28, 2013 12:10 pm

Glad your back, & healing up good. If your bored, look up Smokeys Heat Engine work. Good reading, and will help your thinking on the subject here.
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: Why do carbs seem to do better than EFI for MPGS on 300s

Post #24 by motzingg » Mon Jul 29, 2013 11:02 am

I'm curious whether the improvement in economy from running hot air is related to heat vaporizing the fuel or the hot air being thinner and therefore requiring a less rich mixture.

The other theory is that people trying to gain max mileage set their carbs lean-which results in a drop in power- which you 'get back' when the jetting richens out from the hotter air, thereby giving you more power and requiring less throttle.



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

Post #25 by Harte3 » Mon Jul 29, 2013 12:01 pm

http://www.ford-trucks.com/forums/33927 ... e-6-a.html

8 pages of experiential MPG info on a 300 there...carb and EFI both.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #26 by country fried 6 » Mon Jul 29, 2013 3:29 pm

motzingg wrote:the thing that is interesting is that when emissions engines are running lean, they have to advance the timing. hence the CARB version of the DS2 with electronic advance. I cant imagine those CARB engines were running extreme lean, more than likely just a tiny bit lean. So if the burn happens faster with lean, why does the CARB engine advance?


I believe the advance is because EGR slows the burn, requiring more advance when the EGR valve is open.

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

Post #27 by xctasy » Wed Sep 04, 2013 11:53 pm

Yep. Same down here with our Australian sixes. We found the same thing with the 1986-1988 2-bbl Weber 4.1 alloy head Falcon verses the 1986-1988 EFI 4.1 in our sedans and utlity vehicles. The EFI had the big F150 style 268 degree cam, the stock 4.1 carby had the 256 degree came, one made 131 hp and 232 ft pounds , the other made 164 hp and 246 foot pounds, but the carb was always better mpg gallon wise than the EFI. Each had the same knock sensor, same timing, same exhast and gear ratios, a 50 pound weight penalty for the EFI, and a huge difference in 1/4 mile time of about 1 second over the standing 1320 feet in favour of the EFI. The EFI should have cruised everywhere on less throttle as a result, but it was always 2 US mpg off the carb. Same deal with the earlier years 1983, 1984 and 1985 versions, same loss of mpg, even though those ones ran the same cam.

I know that the EGR helped when it worked well. When it didn't your 4.1 could loose 20 hp and 5 US mpg like in an old 1979 drive article were a much lighter Cortina was slower than the heavier Falcon with the same engine, and it then came right after a long run. The EGR valve was the only explanation. Its gotta be working properly, or you'll loose the gains it can give on the open road cruise.

I'm dealing with the same issues with my 3.3 81 Mustang and its EGR system.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #28 by motzingg » Thu Sep 05, 2013 10:26 am

That's very interesting because I could see a certain economy gain to be had from proper implementation and tuning of the EGR system. Obviously the stock system was designed to make the Feds happy and require little-to-no effort from the consumer, but taking away those restrictions, it seems like it could be dialed in to maximize economy, possibly by using a manual switch.

If i'm understanding the theory correctly, one would

A) set the carburetor for a very lean low-idle, possibly by adjusting pilot jet/air bleed
B) incorporate a method for advancing the timing on demand- much like the emissions 'yellow box' Durasparks do
C) trigger the EGR valve manually or add a manual EGR for a non-EGR big 6

the only issue with A) is that it would be uncontrollable, unless you created an artificial 'air leak' with a solenoid or something. The carb is a pressure/velocity device, but you will be flooding the intake with inert exhaust gas that takes up cylinder volume and goes along for the ride. The problem is trying to explain to your carb that the drop in flow is being caused by EG being leaked into the manifold, and not being caused by a drop in RPM.

the cool thing about using the carb for this, is that you can run it very lean and it wont freak out like EFI, but you run the risk of burning your valves or knocking.

so basically, the theory of operation for the EGR system would be the same, but instead of maximizing the variable of emission chemicals and trying to minimize NOx (from lean burning) or CO (rich) you could re-tune the vacuum set points for a super lean set point in the lower midrange of throttle opening and high vacuum condition, and tune the EGR to max the EG that comes along for the ride.

Instead of thinking of it as chemical modification, you would be using it like a slightly retarded cylinder shut-off.

I dunno, just spitballing here, its an interesting concept and could be as simple as adding a pressure switch and changing some vacuum actuator springs.

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

Post #29 by xctasy » Sat Sep 07, 2013 12:18 am

In the instance above, it was just the EGR that helps, which is always true. Our Aussie sixes met US 49 states Federal 1973, then US 49 states Federal 1975, and never got an air pump ever since we never stooped down to 1980 on ward LA/California emissions requirements. In our old cars, the EGR and two way cat were the only real tools asside from the other 10 minor items like PCV (all the other time hooured Ford IMOCO and Thermactor engine tools before mandatory three way cat and 14.7 feedback loops).

US Ford engines differ due to the cam, ignition and still have a 50 000 mile durabilty requirments, so they are always hobbled down for idle advance, rasied idle speed, extra build in timing drive or cam retard and some other cam and distributor dumbing down aspects. Any time you get TFI igntion and EFI, the fuelie heads were often altered to suit the EFI set up. Early 66 to 74 thermocators were just Hydro carbon detox devices, but after the advent of cat exhast systems, they became smarter hydrocarbon and carbon monoxide reducers as well. With the early I6 Thermactor systems (before cat converters just AIR/Air pump to exhast header air tube operation), the carb is deliberately was jetted 0.003 richer on such units to make up for the peak cfm of the air pump. In later cases, its operation was depending on the O2 sensor for later cars, like on my 81 Mustang 200. Other times its uniform all ways on with only part throttle diverter valve operations. Since 1969, NOx was a major issue, so air pumps ahve been in tandem with a compression ratio drop,

This setting means that a modern 1972 to 1996 sub 10:1 compression engine with thermactor won't show performance boost when that part of the emission system in played with. Most of the sometimes massive performance drops on AIR pump engines were due primarily to low compression for 87 AKI fuel and then the distribitor and cam timing that went with them. A point of note is that the dirty non emissions verses clean air EGR and AIR equiped engines may have lost 50% of there power, and 25% of the mpg figures in the 70's and 80's, but its rare for that loss to have to ever been due to EGR or AIR pump. A golden example was 205 hp net from a 1978 German 2.8 Benz engine on 9.2:1 and 97 AKI, then just 142 hp on 8.3:1 and AIR and EGR when in the USA or Australian markets. A 16.9 second quartmile car suddenly does only 19.2 seconds, and only 23 US MPG instead of 28. And you can bet when the EGR and/ or AIR was unhooked, the fuel consumption was even worse than that, as the base cam and distribtor timing was never able to be amped back to non emssions levels.

The 240 and later 300/4.9 F100 /150 engine is able to see similar 50% performance and 25% fuel economy improvements if the full emission package is removed and the engine optimized with 93 AKI, but normally, there is only a 10% loss of fuel consumption and power when any emission engine is optimized as a compliant package. It then failes to become a stock engine package. It may be that US Federal and Cali emissions might have a lot to answer for, but anytime you remove an emission system, you become a potential gross polluter, and a truck can then make an insane amount of idle HC, NOx and Carbon Dioxide and Monoxide when you fiddle with them. I support CARB rules becasue untill you do a sniffer test, you don't know how much an emissions equipment removal hurts emissions.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #30 by Lazy JW » Mon Sep 16, 2013 6:54 pm

BIG 6 farmer wrote:Back in the day, about 1980 or so. Alot of guys with newish F150s 300 sixes. Claimed to pull 20-27 mpg, on a good Hyw. trip. But the speed limit was 55 still...


Yes they did. BUT....

Those pickups had the DFC (Dreaded Feededback Carburetor) along with the stock intake/exhaust manifolds that were bolted together for heating the intake; also they had the factory heated air cleaners and fully functional EGR systems.

And they also had extremely tall gearing. Some of them came stock with 2.47 rear end gears plus the Overdrive 4-speed transmissions, resulting in something around 1200 rpm at highway speeds. Very miserable to drive.

My 81 F-150 averaged 19+ mpg for 60,000 miles over a three year period. I recorded every gallon of gas and every mile it was driven, and this represents a true average of winter, summer, idling, whatever. NOT just a one-time trip down the Continental Divide with a tailwind. I checked the odometer and it is very slightly off, but in the direction that means it actually gets a tiny bit BETTER than the reported 19+ mpg. I have never encountered anyone who can make a similar claim of comparable mileage.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #31 by motzingg » Tue Sep 17, 2013 3:54 pm

well, that's round about what i'm getting at. you have the OEM's trying to hit two major targets with emissions- NOx and CO. The NOx is formed largely at high temp/lean burn conditions where there is excess oxygen to combine with available nitrogen, and CO is forming at low temp/rich conditions where there is not enough oxygen to bond two per carbon.

The OEM's played the game by jetting the (highly fallible) carburetors on the rich side, running low compression and recirculating exhaust gas to slow down the burn and reduce NOx emissions, then ran an air pump to 'burn' the CO into CO2 later down the exhaust pipe. They were more concerned with making sure every car under any circumstances was always in compliance with the law, and would rather see fuel get wasted than run the risk of not passing a test.

So by perverting that logic, you can run lean instead and use the EGR as an inert gas to take up volume and go along for the ride, without making you too lean. You would be producing more NOx, but could safely run at low power (high vacuum) levels on much less fuel. Fuel savings being the percentage you are jetted lean compounded by the percentage of intake that is mixed EGR and not coming through the carb. You could keep the mains jetted large but would have to adjust the midrange jetting to accommodate the lean cruising, or employ some kind of air bypass valve that would fool the carb and selectively lean it out.


As for the actual emissions, i'm not trying to make indian dudes on the side of the highway cry or nothin' but as long as the engine is running well I'm not going to loose sleep over the emissions. I've got a narrow band o2/lambda sensor that is getting installed as soon as she is ambulatory enough to drive into work where the welder is.

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

Post #32 by E4ODnut » Fri Sep 27, 2013 12:54 am

Emissions concerns aside, for best economy keep your mixture as lean as you can without a lean stumble, keep your revs low and your manifold absolute pressure high. It works. The 300 thrives on low speed, high load.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #33 by THE FRENCHTOWN FLYER » Fri Sep 27, 2013 9:19 am

E4ODnut wrote:... The 300 thrives on low speed, high load.



...as do all internal combustion engines. The trick, of course, is to keep them tractible at low speed / high load conditions, which our 300s do quite well.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #34 by Lazy JW » Thu Oct 03, 2013 4:00 pm

THE FRENCHTOWN FLYER wrote:
E4ODnut wrote:... The 300 thrives on low speed, high load.



...as do all internal combustion engines. The trick, of course, is to keep them tractible at low speed / high load conditions, which our 300s do quite well.


.... and my TorqueMotor does that just a leeeeetle bit better than most.... :D
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #35 by THE FRENCHTOWN FLYER » Thu Oct 03, 2013 11:14 pm

I can believe that. If you ever popped the clutch in that I'd probably feel it back here in Frenchtown.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #36 by turbo2256b » Fri Oct 04, 2013 9:47 am

THE FRENCHTOWN FLYER wrote:Short answer: EFI engines have to cruise at an A/F ratio near to 14.6:1 so the EGO sensor will function. Carbs can have an A/F ratio above 15:1 at cruise mode so they will possibly get better highway fuel economy, even though the throttling processes associated with a carb venturi will increase pumping losses.

Not so it is set to provide different A/F ratios depending on load up to aroud 75% some more some less depending on engine build after max load is reached it goes into WOT which is a totaly different function in the ECM. Timing is the same sort of set up there is load then into WOT. There are a lot of other functions that input into these.

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

Post #37 by turbo2256b » Fri Oct 04, 2013 10:08 am

argo wrote:I have never understood why EFI is less fuel efficient on these engines than a carb setup. It baffles me because it seems to be an anomaly. EFI tends to be more efficient on almost any other type of engine. Does it maybe have something to do with the cam timing more so than the fuel delivery?


EFI didnt improve the economy on the 460 either. Most engines such as the 460 from 73 or 72 onward had retarded cam timing to help with emissions(460 was retarded 8*). A lot of things done early in immision engines were like experements a learning curve it was all new to everyone. When they went to EFI it changed back to straight up. Not sure about timing in the 300 six when it went to EFI.

Part of the issue with the 460 never improving was intake and exh were never redesigned for it. At Ford Advance engine Design we did an experimental redesign the intake around the time the V10 was being tested. Our 460 beat it out in production cost, performance and economy. We were told to drive it ino the pond infront of the POEE building as it was not the direction Ford was taking.
Think the 300 kindof facing. We did a cross flow head design a pallet of heads were made ,50 maybe dont know if they were even machined and tested (always wanted to grab one and test it out).

Bottom line they were both slated to go out of production in a couple years so no one cared about improving them.

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

Post #38 by turbo2256b » Fri Oct 04, 2013 10:34 am

EGR was introduced to run vacuum advance without over advancing. Without EGR vacuum advance might only be limited to 5* instead of 15 or more degrees. A internal combustion engine at cruse conditions inherently is a bit rich and has residual fuel in the chamber. To help burn this fuel extra advance is added which helps with economy. The combustion chambers with the newer fuels got to hot to use vacuum advance and meet emissions so EGR was added to reduce cylinder temps so vacuum advance could be increased to reduce emissions and improve fuel economy over not having it although possibly not as much as if fuel went back to higher octain leaded stuff.

I did ,while tuning my 302 in my 87 Grand marquis, find a EGR valve that had a blunter pintial in it and swapped out the more pointed smaller orface stock version thinking it might increase EGR and help with economy. Could never realy prove it did. With all the other changes done before and after did end up with 22 MPG in town and 32.9 highway.

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

Post #39 by motzingg » Fri Oct 04, 2013 10:41 am

:shock:

thats some straight up willy wonka stuff right there. a pallet of 50 crossflow 4.9 heads sitting in a warehouse somewhere next to the arc of the covenant!

I cant even imagine how awesome working on engine design at an OEM must be, every time you guys tell stories it just blows my mind.


EDIT: is there any other info you could provide on getting 32 mpg out of a 87 grand marq. ? I'd love to hear it

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

Post #40 by ludwig » Fri Oct 04, 2013 2:53 pm

So I was watching Car Wankers or whatever that show is where they buy some car cheap and then a stubby English guy with dark hair yells at you while EDD tweaks the poppets.

They had a '76 Maserati (I thinnk) and they called in a tuning specialist. He used a flow meter on each of all EIGHT 1bbl carbs, one at a time. He had to turn the idle down to the same or similar level on each carb and balance the inflow rate x 8. Then they needed TWO guys to set the timing: one under to read the balancer mark and one on top to back off the rotor . Once he got the flow, idle and timing in place, oddly enough, the thing ran better and used less fuel.

BTW, he backed the timing off from about 30* to 14*. Someone had been bumping it up as his performance degraded due to carbs out of adjustment. I can see where EFI and electronic ignition would make a huge difference in EIGHT carbies.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s

Post #41 by turbo2256b » Fri Oct 04, 2013 3:50 pm

Therre are EFI systems with IR setups that look like Webbers possibly they would do better but its pricy. They will out do a single dual style EFI system.

http://www.hilborninjection.com/


Using a Carb well set up with a programable ignition system or a coil pack programable system both can be used with A MAP sensor (its like vacuum advance). Non boosted works with a 1 bar sensor.

Realy the biggest differance between EFI and carb is the abilty to do things with timing that cant be or difficult to do.

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

Post #42 by xctasy » Sat Jul 27, 2019 7:30 pm

ludwig wrote:So I was watching Car Wankers or whatever that show is where they buy some car cheap and then a stubby English guy with dark hair yells at you while EDD tweaks the poppets.

They had a '76 Maserati (I thinnk) and they called in a tuning specialist. He used a flow meter on each of all EIGHT 1bbl carbs, one at a time. He had to turn the idle down to the same or similar level on each carb and balance the inflow rate x 8. Then they needed TWO guys to set the timing: one under to read the balancer mark and one on top to back off the rotor . Once he got the flow, idle and timing in place, oddly enough, the thing ran better and used less fuel.

BTW, he backed the timing off from about 30* to 14*. Someone had been bumping it up as his performance degraded due to carbs out of adjustment. I can see where EFI and electronic ignition would make a huge difference in EIGHT carbies.



Actually the 1973 Lamborghini Urraco P250S, the underpowered early version before it got 3liters.



With quad Weber DCNF carbs feeding the V8, it had this process to follow from 28 to 33 minutes



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

Post #43 by Pathines » Wed Aug 21, 2019 5:52 pm

I can't think of a single instance where carbs are more efficient than or produce more power than fuel injection.

I've had many carb equipped vehicles now have a number of FI vehicles. In my opinion, FI is much more efficient than carbs and easier to adjust as well. You just have to know what you're doing to keep it tuned.

I'm about to purchase an FI truck with the 300/4.9L engine. It's exactly what I want and would never consider replacing the FI system.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s?

Post #44 by xctasy » Wed Aug 21, 2019 8:31 pm

Welcome Pathines!


In terms of brake specific fuel consumption in pounds of gasoline per horsepower, many, many , many carb engines beat Mechanical Fuel Injection and EFi.

This has been the case since the first EFi engines in the late 60s to current engines.

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

Post #45 by sdiesel » Thu Aug 22, 2019 1:48 am

....and my pointless point to be made is, it's more than just fuel delivery, it's maintenance.
was it bunky knudsen who said he wanted to. build a car so well they could weld the hood shut?
at any rate many owners never maintained their EFI engines due to the seemed complexity , and thus just drove it.

thus many EFI , as they aged underperformed their carburetor counterpart engines?

the inline is back in vogue with many manufacturers.
let's see what 30 years of technology will do for this lovely engine.
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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Re: Why do carbs seem to do better than EFI for MPGS on 300s?

Post #46 by xctasy » Thu Aug 22, 2019 2:28 am

The extra 30 hp the EFi Falcon gave the Cross flow took 3 mpg off the 62 mph fuel figures in 1985. The port 1986 EFi 5.0 lost hp and mpg over the 4bbl 1985 5.0 V8 Mustang.

The 1978 to 1985 150 and 160 Bosch Ķ jetronic 2.8 Cologne used more fuel than the 1977 to 1981 138 hp 3.0 Essex V6 and made less mid range torque. The Ferraris with Bosch K jetronic lost 40 hp verses the quad Weber versions of the 308s, 512s and 400s...and they said it was just for emissions.



The Alfa Romeo Spica injected Montreal and 1980 US Alfettas were thirstier by far...the downgrade back to Webers for Jalápas and Countaches whilst Ferrari were going Bosch injection was for performance.

The whole growth in port EFi was in getting aromatic hydrocarbons out of the overnight LA Basin emmission cycle purge session. Renault did it by just adding a turbo and keeping the 1bbl Solex carb sealed...job done with more horsepower.

Lotus kept the Esprit Turbo carb version emissions legal with great economy and off boost performance with a very low compression ratio. The EFi version with high compression was more powerfull, but signifcantly more thirsty. The conversion to injection for the JDM Mini Cooper 1275 stole many miles per gallon. The same with the unleaded fuel V12 Jags verses the early  V12 XKE.

Many, many examples of the death of great dollops of horsepower, mid range torque and highway and city cycle fuel consumption with the advent of single throttle body M and EFi.

The Rover 3500 and TR7 V8 never showed those claimed 11 extra hp over the 137 hp Twin Stromberg CDS175 carb engine.

The fuel injected 460 was a great lumbering ediface of thirst and poor performance compared to the 4V 370, 429 and 460s with the Holley 4195 4bbl. Although never a power house, the 132 hp 2300 2bbl carb turbo Mustang and Capri of 79 and 80 showed that adding a turbo was better than adding EFi.


Turbos on carbs worked better than injection, and blow through carb instalks like Paxton and CARB approved blow through turbo kits were better options than injection for the first 5 years into the 1980s.

The issue with single or dual runner EFi by Lucas, Bosch or Nippendenso, Kugelfisher or AE Brico or the Cosworth Vega Bendix system was about making it work to control air fuel.

Fords feedback 1 and 2bbls were very efficient, but didnt show any gains over the stock non managed earlier 300s and 302s; Importantly, the rare 351 HO options with the Variable Venturi 2bbĺ for Police squad CVs and GMs or the truck 4bbl F150/250/350 were fine performers compared to the bank fire 5.0 and 5.8s with there big thirst. The CV/Grand Maquis port EFis 5.0s werent as frugal as the 1980 and 81 AOD 165 or 175 hp versions. The issue was the need to knock off hydrocarbons, and the early Ford EFis were just tragic schmozzels of upper intake experinentation.

The bank fire and sequential EFis in 5 liter and 5.8 form eventually had some really good gains in power and torque, but they needed head and cam changes to find the best mpg and emissions. Independent ruuner carbs were never a US thing....the Italians and English mastered that, and then had a heck of a rob getting the power keveks back with Mechanical or Electronic Injection.

The Germans nailed EFi, but it was a service disaster which only Detriot fixed. The twin 3bbl Porsches had to get a turbo or more capacity to cover off the Bosch K Jetronics lack of peak power.

The Weber IDF versions of good Individual Runner intakes were far stronger than the 2bbl Solex carbed emmisions vehicles in the Lamboghini Urracos and 911Ts

The carbs govern how well the power is made...the European twin Weber versions of the Ford Escort RS2000 had far more power than the EFi Ford Sierra and Saphire and Scorpio 2.0s and more hoof than the Solex 2x2bbl RS2000s. The French decided that turbos were more effective if injection was needed for emissions. The destroked 2.4 liter Alpine À310 Turbo might have shown just how anemic the 2.85 PRV Bosch MFi V6 was. The port EFi Toyotas and Nissans and Mazdas show a lot of thirst compared to the lower power 2bbl carb versions. Mitsubishis Turbo silent shaft cars were simarly very thirsty with karmen vortex Twin point or ECi Multi EFi. Lots of examples here....nearly every EFi engine, and most Mechanical Port Injection engines.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s?

Post #47 by THE FRENCHTOWN FLYER » Thu Aug 22, 2019 8:29 am

Well there's something we can agree to disagree on.

Carbs require a pressure differential to function, i.e., intake manifold vacuum.
We typically saw about 1.5 in. hg intake vacuum at peak HP WOT. With EFI no pressure differential is needed to make it function so at peak HP WOT the intake vacuum is less than 1 in. hg. I typically saw about 0.8 - 0.9 in. hg. on the dyno and much of that was due to the noise attenuation restriction in the air inlet ducting.

Add in the fact that chokes on carbs were notoriously finnicky and less than perfectly reliable (remember having to give the choke cap a twist when the seasons change? and all the carb air heater ducting and choke tubes that rotted away and were largely ignored by portions of the motoring public? rotting vacuum lines, etc?) I would say that there is good reason the automobile and motorcycle manufacturers have embraced EFI. Not to mention boats, snowmobiles, tractors, etc.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s?

Post #48 by MechRick » Thu Aug 22, 2019 12:58 pm

The one barrels seem to get fantastic fuel economy. I remember a sign in the Lincoln-Mercury dealer I worked at in the 80's had a sign displaying the Capri stating "The cat's full of surprises" showing an EPA highway MPG rating of 40 mpg. 2.3L manual trans 1 bbl. That was back when the speed limit was 55 MPH and no one was in a big hurry to get anywhere.

Which brings me to an overlooked point: We don't drive vehicles like we did in the Eighties.

Even my old '81 F150 4x4 that I managed to eek out 19 MPG on was driven like one drives a 15 year-old (at the time) truck. Carefully.

My modern EFI sixes got worked. Hard. 80 MPH up and down hills, WOT pulling a trailer, etc...conditions that would have made the carbed '81 puke it's coolant all over the road.

EFI Ford cars used to go into an open loop strategy on the highway running leaner than stoichiometric. Not sure if that feature ever made it into the trucks.

You can build a Megasquirt for slightly over $200. Scrounge a factory EFI manifold, injectors from just about anything, fuel pump, a cheap wideband, and have a completely tuneable to any fuel mixture or timing table you want EFI setup for probably less than the cost of a Holley 390. For me, I wouldn't even consider a carb.
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Re: Why do carbs seem to do better than EFI for MPGS on 300s?

Post #49 by xctasy » Thu Aug 22, 2019 2:43 pm

That junk DNA that lean cruises at greater than 14.7 on the o2 sensor existed for a while on some bin EECIV definitions, but it was later deactivated, then removed. Federal mandates were flunted by Toyota (Air fuel ratios on EFi cars in the early 80s, 16.2:1) and Mopar (Electronic Lean Burn from 78 to 81 had 16.2:1 ratios under part load)

The 1980 Foxes got a Tremec made T140 5 speed "Hook Shift" option starting early 80 model year. The 3.08:1 axle got changed to 3.45, the carb then got down graded to 23 mm primaries from 26 mm. The 2.3 Holley Weber went up 4 mpg to 38 mpg HighWay before all the EPA figures were then downgraded in 1982.


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see https://fordsix.com/viewtopic.php?t=76051

My 81 Mustang 3.3 automatic was downgraded from the 8.4:1 1980 spec E0 head to a 1963 C3 coded 170 closed chamber head with an 8.9:1 compression ratio, and it never got better than 22 mpg US at 55 mph. Mtang and Capris with the 4speed T4 or SROD 3.3 engines were rated as 30 mpg at 55 mph as a manual,

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This was 4 mpg off the downgraded 1982-1986 2.3 5speed figure of 34 mpg.

Ford lost 4 mpg with the later four cylinder 2.3's due to some other reason. It wasn't emissions and they didn't drop the 3.08 axle ET78 4 speed version.

Fords 1bbl downgrade in 1983-1986 pickups (2.0/2.3/4.9) and Fox 2.3's from 1983-1988 or so were very economical, and were feedback, with the Rochester/Carter style Mixture Control Solenoid operated by Pulse Width Modulation via MCU or EECIV. TFi had proven imporovements in mpg.


The work done on highways and give and take or Hail Mary merg zones on interstates, is a debit against the EPA mpg figures, which don't allow for traffic flows and densities. A lot like Insurance premiums on rated horspower to weight, if Automakers felts the hard edge of Franco like incursions, they'd just change to ratings from some other place on the power curve instead of saying my 3500 pound Boss 429 has 425 hp at 5800 rpm, it actually has 375 hp at at 5200 rpm. Half the story worked real good from 1968 to 1971. Or rating the G code Tunnel Port 302 at 240 hp when the J code made just 230 hp.

if its hp insurance premioums at the 10 pound per hp level, then car makers just dropped the hp to a lower quoted point on the hp curve, and pleaded no contest to the 4250 weight limit a 425 hp had to get. Like a 454 Chevelle, they either added weight, or fudged power down.


In any case, EFi and MFi lost out in power over ITB Carb systems in every case, and 1 and 2-bbl carb cars were often better than port EFi versions. Period.
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XEC Ltd ICBE's Inter Continental Ballistic Engines-
FAZER 6Bi (M112 & EEC5) or FAZER 6Ti (GT3582 & EEC5) 425 HP 4.1L/250 I-6
FAZER 6V0 3x2-BBL Holley 188 HP 3.3L/200 I-6 or 235 HP 4.1L/250 I-6
X-Flow Engine Components Ltd http://www.xecltd.info/?rd=10

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

Post #50 by Pathines » Thu Aug 22, 2019 3:01 pm

MechRick wrote:
My modern EFI sixes got worked. Hard. 80 MPH up and down hills, WOT pulling a trailer, etc...conditions that would have made the carbed '81 puke it's coolant all over the road.

EFI Ford cars used to go into an open loop strategy on the highway running leaner than stoichiometric. Not sure if that feature ever made it into the trucks.

You can build a Megasquirt for slightly over $200. Scrounge a factory EFI manifold, injectors from just about anything, fuel pump, a cheap wideband, and have a completely tuneable to any fuel mixture or timing table you want EFI setup for probably less than the cost of a Holley 390. For me, I wouldn't even consider a carb.


I don't have current experience with the EFI engine (yet), I'd be shocked if any carbed engine could do better that the EFI 4.9l engine IF the EFI engine is well maintained.

I looked at your engine build thread, MechRick, well done I'd say.
'93 F-150, 4.9L, 5-speed, stock, lots of miles

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