How Much Fuel Economy Does EFI Gain?

Engine, Transmission & Driveline

  1. Henrius

    Henrius Member FCBO Gold Member

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    A few posters have converted their B blocks to EFI, and commented favorably on engine running improvement, especially when cold.

    But what have been the gains in overall fuel economy, if any? Old C bodies with cast iron blocks are still a lot of mass to accelerate, and they are not exactly aerodynamic either.

    The best I've ever gotten has been 14mpg on the freeway at about 50mph, but most of the time it is more like 11-12mpg on both my 65 Fury and 72 Newport. I haven't kept the Newport original, so would not be adverse to converting to EFI, if there was a decent fuel economy gain.
     
  2. I gained 4 to 6 in my 72 fury 360 originally got 16 with efi 20 to 22 depends on speed and if there is a head wind
     
  3. Wile E Coyote

    Wile E Coyote Super Genius FCBO Gold Member

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    Just to talk to the fat girl at the dance, I'll strike up a conversation. I'm going to bet it only delivers 3 more MPG. B-body, C-body, A-body, I'll bet it doesn't matter. I say that based on my 84 Crew Cab long bed dually, auto, 4:10 gears. I get 6 to 7 mpg; empty, towing, trailer empty, trailer loaded, it doesn't matters - its 6 to 7 mpg period. BUT, I'll bet the real advantage is the easy start without the cold-engine-choke-hassel.
     
  4. SPF Required

    SPF Required Member

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    I installed a FiTech on my ‘68 300, and unfortunately I cannot easily measure my MPG because my odometer is shot. But... what I can say is the performance is through the roof. It is super responsive never makes me feel like it is going to stall when idling. It is awesome at cold starts and you can feel the CPU getting everything dialed in on hot starts.

    I know I went against the grain for some on this site by making a restomod out of my engine, but I couldn’t be happier and this car has never felt more reliable.
     
    Last edited: Jun 12, 2018
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  5. Turboomni

    Turboomni Senior Member FCBO Gold Member

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    I am not knocking efi,,actually how could you for better engine management, but my old 440 in my 69 FuryIII went from 11 mpg to a hair over 15 tooling around town on points with proper timing ,vacuum advance and carb tuning [at least according to my odometer}.
     
    Last edited: Jun 12, 2018
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  6. CBODY67

    CBODY67 Senior Member

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    I've long contemplated an EFI upgrade on a few of my cars, but the cost is still a good bit more than a new carb. I can't see saving enough fuel to justify over $1000.00+ in expenses.

    Computerized EFI will optimize the fuel mixture for best performance. It can cure many ills of an ill-tuned carb/intake/cam combination, I suspect. I suspect that THAT will be where most of the fuel economy increase comes from. BUT if you set the mixture parameters too rich, no real savings might result. The optimum fuel mixture is 14.7:1 for non-ethanol fuels. Probably needs to be more like 14.1:1 with E10. Cruise air/fuel, that is. Idle will need to be lower, possibly.

    One thing needed for the self-learning EFI is a compatible distributor! More costs not in the kit. Although some can control ignition timing internally. Something else to consider.

    When the speed limit changed to 55mph, nationally, I was keeping tight figures of highway mpg, using % of throttle, rpm, air/fuel ratio, and such to figure each segment of my 290 mile trips home from college, circa 1973-4. The car was a stock '66 Newport Town Sedan 383, with a 1970 OEM Holley 2210 carb. 55mph segments came out to be right at 20 mpg. 2.76 axle ratio/H78-14 tires. Later higher speed limit trips dropped to about 17mpg. Before that, when newer, the highway mpg average (70mph speed limits) was about 17mpg. Local town stuff was more like 14mpg.

    During the fuel crisis related lower speed limits of the earlier 1970s, Fenner-Tubbs Chrysler in Lubbock took cars in their new car demo fleet on a mileage check. They filled the tanks at the Shell station across the street from the dealership, then took the cars south to the edge of the Caprock, turned around, came back, and topped off the tanks. 1974 NY 440, 20.66mpg, Newport 400 2bbl, 20.33, GFury 360, 19.6. When I put a "matched" TQuad/Torker383 on the same '66 Newport 383, allegedly calibrated for a '70 383 4bbl, never got past about 15mpg highway, no matter what, or with different primary rods (from the TQ Strip Kit) I tried, seeking to match the '74 fuel curve). More perf, but no real fuel economy advantage over the earlier 2bbl.

    To me, in reality, electronic EFI is just a better fuel-mixer than a carb can be. Performance happens as soon as the throttle is opened, not after the opened throttle results in increased air flow through the carb. That is where the better throttle response probably comes from.

    Key thing about carbs is that it can be hard to really know the ultimate-supplied air/fuel ratio without putting the vehicle on a chassis dyno. A 13:1 ration can seem to be a 14.8:1 (stoich), when it really isn't, for example. Many like to "jet rich" for allegedly best performance, but this takes a toll on cruise mpg, as can deeper rear axle ratios and such. That "out of the box" carb might install and run well, but is it really as optimum as it could be for your car? With fewer techs really knowing how to work on carbs, probably best to have something under the hood they at least understand. Not that they'd know how the particular EFI system works of is calibrated.

    The other place where electronic EFI is better is in the "coast" mode, where the factory units basically shut-down fuel delivery when it isn't needed. A carb can't really do that to result in the OEM EFI "coast" of 99mpg.

    EFI will be MORE critical to driving style, by observation. Each time the EFI throttle is opened, more fuel into the air flow happens, no matter what. On a carb, when the throttle is opened, it takes increased air flow through the carb to get fuel from the float bowl into the throttle bores. UNTIL you get into a newer car with a readout of "Instant Fuel Economy", then watch it as you drive, you don't understand how critical throttle input is into the fuel economy delivered by the vehicle. It's all there in front of you, in real time. A 20mpg 60mph steady-state cruise can instantaneously become an 11mpg acceleration with not much added throttle, or when going up a hill with the cruise working. I strongly recommend this, even if you have to rent a car to do it. Quite revealing!

    The referenced Chevy 454 pickups did get that mpg, from the factory. With a 4.10 gear, they'd "work", but they were thirsty. No black smoke from the exhaust pipes (from a too-rich mixture), either! Ford 460s were similar in similar vehicles.

    So, the self-learning EFI can be a good thing to do for many people. Can save some fuel, too, in some cases, just don't expect miracles for the money spent.

    CBODY67
     
    Last edited: Jun 13, 2018
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  7. Turboomni

    Turboomni Senior Member FCBO Gold Member

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    I have often wished I had two wide band O2 sensors, one on each bank of cylinders on my Fury. It would make tuning the carb so much easier and factual with data I can see.. The efi systems I see offered for our v8s is a closed loop system of course but only one O2 sensor is used which is kinda too bad. It just assumes the other bank is acting exactly like the one it is monitoring if you have dual exhaust.i have often wondered how good a tune I could get on a carb with wide band O2 sensors to see what is going on. Then accurately tune the carb jets,metering rods etc. To me at.least it sounds fun.
     
    Last edited: Jun 13, 2018
  8. 78Brougham

    78Brougham Old Man with a Hat FCBO Gold Member

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    You may want to check out this kit. The MG, Jag, etc..... guys use it and seem to like them on some of the forums I'm on. The side draft Stromberg, SU, Weber carbs etc can be a bear to keep in tune sometimes.
    Colortune
     
  9. live4theking

    live4theking Old Man with a Hat

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    That's an interesting little too. I might have to look at it a little closer. Do sell them out of the truck?
     
  10. 1978 NYB

    1978 NYB Old Man with a Hat FCBO Gold Member

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    I have watched a few EFI conversions on this forum and other forums. Even though EFI is cool and modern I just think the installation and mapping are still a bit complex compared to the tried and true painless Eddie or a Holley Quick Fuel carb. I have an Eddie on my 78 NYB and it sat for 6 months and started in 5 seconds. Even the battery had enough juice to start the car.
     
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  11. commando1

    commando1 Sergeant at Arms FCBO Gold Member

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    Converting an old NA engine to FI is too often done by people who can't tune a NA engine.
    Not knocking anyone here. Just in general.
     
  12. 1978 NYB

    1978 NYB Old Man with a Hat FCBO Gold Member

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    I guess the install could be a little easier using an external electric fuel pump. I just don't see the minimal gain in mpg as a reason to convert to EFI.
     
  13. jct

    jct Senior Member

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    Then there's the rumor of the engine running like crap on a dual plain intake manifold with the tbi
     
  14. Turboomni

    Turboomni Senior Member FCBO Gold Member

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    You could uld say the same about points and electronic ignition too although the cost of converting is not as high and the lack of maintenance as a result.
     
  15. commando1

    commando1 Sergeant at Arms FCBO Gold Member

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    Points were a constant nuisance.
    Points on a SB was a pain in the ass.
    DUAL points on a SB just plain sucked.
     
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  16. Turboomni

    Turboomni Senior Member FCBO Gold Member

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    Yeah they can be a nuisance especially compared to the GM (I think) with the sliding door on the dizzy cap and just stick a hex wrench in and adjust the dwell. I just like the prehistoric mechanical machinery opening and closing like a small textile factory and the fact I can still get points easily and cheaply. I like the tinkering and it runs well. When I do tell people who ask about the car that she runs points and drum brakes sometimes their jaw drops. Or they have no idea what i am talking about lol.
     
    Last edited: Jun 13, 2018
  17. 67Monaco

    67Monaco Senior Member

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    Most likely the later not the former.
     
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  18. Yes my 360 would surge with a dual plain so i switched to a single plain and it stopped
     
  19. 78Brougham

    78Brougham Old Man with a Hat FCBO Gold Member

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    No I don't, just heard about it on my forums when learning to tune my SU's.
     
  20. Yatzee

    Yatzee Active Member

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    After reading all of the above comments, I've come to the conclusion that there are definitely two camps on this subject. It seems many people are against the new technology and many pass judgement and don't even have one installed. Others are like sheep and just follow the rest of the flock but if the unit was free, would install one in a second. I have three classic with EFI and when I did the last one I put the carb in the garbage can with a smile on my face. Good riddance! The secret to improved mileage and all round fuel savings is found in the A/F ratio and condition of the ignition components and timing. On two of my vehicles I gained 6 mpg overall and the third rendered 4-5 mpg. On all three I could not help but notice how much longer the fuel in the tank lasted than before installation. There is no reason why you would have to monitor dual exhaust with two O2 sensors, that's for multi port where you might have a degrading injector thus the second sensor will send a fault code and warning light for that bank. The latest EFI's, even the cheap ones, walk all over carbeurators in every category of operation and the upside is that they actually learn your driving style and always try to optimize fuel usage at the same time. I understand that these units aren't for everyone for various reasons (financial, skill level, knowledge) but one thing is for certain - installed properly you'll never look back.
     
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