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Fuel Injection Versus Carb Mileage

Discussion in 'The Garage' started by ntx78k5, Aug 19, 2005.

  1. ntx78k5

    ntx78k5 1/2 ton status

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    I did a search and didnt really get what I was looking for.

    With Gas prices being what they are and being in the freight business I know they are only going to get worse. Probably $3.25-$4.00 a gallon by end of 06.

    My question is with the added expense is anyone seeing a great increase in mileage if you upgrade to a fuel injection set up. I am getting around 8 now all miles.

    Thansk for any help you can provide
     
  2. resurrected_jimmy

    resurrected_jimmy 1/2 ton status

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    you gotta give u smore info than that.......what type of vehicle, engine size, tire size, gears

    but in answer to you question I saw an improvement in milage going from carb to efi on my 76 k5
     
  3. MTMike

    MTMike 1/2 ton status

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    I'm running a Holley Projection 4D EFI system on my Stroker and get about 5mpg with it :doah:
     
  4. Burt4x4

    Burt4x4 3/4 ton status

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    Fuel injection in general is more efficent than a carb, so genericly speaking Yes you will get better fuel economy. Ofcorse, just like a carb, all bets are off if you drive around like a madman floring it around every turn.
    Also keep inmind MPFI is more efficent than a 'batch fire' EFI so research before you spend $$ for the upgrade.
    FI is AWSOME for throttle responce too so alot more fun to drive with a healty engine :D
     
  5. 6.2Blazer

    6.2Blazer 1/2 ton status

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    In general you should see a slight increase in fuel mileage when comparing the same engine with both a properly tuned carb vs. a properly setup EFI. However, keep in mind that depending on how much it costs to do the conversion it may take a long time before the increased fuel mileage even pays for itself.
     
  6. ntx78k5

    ntx78k5 1/2 ton status

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    78K5 4" lift with 35's 350V8 with an RV cam TH350 and a 203T case.
    I am running a stock quadrajet and a Edlebrock intake manifold designed for greater tourqe numbers. Truck has 342 gears.
     
  7. shane74

    shane74 1/2 ton status

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    There is part of your problem. You should be running at least 4.56's w/ 35's. Especially with that tranny/t-case combo.
     
  8. loafer

    loafer 1/2 ton status

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    I went from 13mpg highway to 15mpg when I switched from a 650 Edelbrock to a Holley Comander 950 600cfm TBI set up. I'm running a 350 with 33" BFG MT's, 700R4, and 4.10 gears.

    My fuel economy numbers inlcude a 10% correction factor for the gear/tire combo I'm running; the odometer reads 10% more miles than I've actually gone, as-calculated milage avereaged 13.7mpg carb and 15.75mpg EFI on the highway.

    Getting the EFI tuned correctly is key for fuel economy and you will only see benefits if you run an o2 sensor for closed loop operation.

    Fuel economy was not the only reason I switched though; I was tired of stalling on steep climps, and hard starting in the winter. What finally pushed me over the edge with the carb was a bad engine fire while driving up a steep mountain trail.
     
  9. fatbob

    fatbob 1/2 ton status

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    "You should be running at least 4.56's w/ 35's."
    Sorry but I don'y agree. You may not have much pickup when you start off, but when you are rolling down the road, your RPM's will be nice and low. If you put those gears in, you would have great pickup, but you would be sucking up the gas trying to do 60MPH on the freeway.
    But back on topic, I think FI can do marginaly better than a good running carb, but not enought to justify the cost of converting. And while Fuel Injection can be more responsive, it is more expensive to repair. If your fuel pump goes out on carbed motor, $20 and 30 mins will get you rolling again. With FI you first have to figure out if its the pump, relay, regulator, or injectors, and then you pay a bit more for parts. :doah:
    I have a carbed 3/4 ton k20 = 11 mpg
    also a TBI crewcab k3500 = 9.7 mph
    I'm leaviing both fuel systems as they are.
     
  10. loafer

    loafer 1/2 ton status

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    For fuel economy 4.10's are better choice with 35's and no OD.

    The full-time 203 t-case will kill fuel economy as well.
     
  11. 6.2Blazer

    6.2Blazer 1/2 ton status

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    I agree with everything he said, and should have included more in my original post.

    - I would not bother converting over to EFI simply for fuel mileage improvements........but the increase in driveability, easy starting, flawless operation on grades, etc.... are definitely worth it

    - If fuel mileage is the primary concern than you really don't want 4.56 gears w/ 35" tires and a non-OD tranny. While it would be a good combination power wise and quite acceptable on the highway, that's a little to low of a gear for optimum economy while cruising down the highway.
     
  12. CyberSniper

    CyberSniper 1/2 ton status Premium Member

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    Well, the TH350 doesn't lock up, the 203 is full of parasitic losses, and if you're spinning anything in the front end you're losing even more.

    One of the best ways to get an increase in fuel economy is to make what you've got work properly. That means an ignition tune up and a carburetor tune up. It means converting the NP203 to part time, running manual locking hubs, and putting fresh gear oil in the rear axle.

    For peak fuel economy with that setup you'd probably be better off with 3.73s. The torque converter not locking up and the ****ty first gear really hurt you.

    I get the same fuel economy at 65mph whether I'm in third gear or fourth (overdrive). In third gear the motor turns about 2400rpm but isn't working at all and has peak vacuum (which usually means peak efficiency). In fourth gear it turns around 1900rpm and has very low vacuum and unlocks as soon as there is an increase in load.
     
  13. ntx78k5

    ntx78k5 1/2 ton status

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    I've done all but the switch to part time 4x4 as I have no idea what that intails and the gear swap. This started out as a hunting rig and as all things I've started messing around with it and 4wheelin when I am not hunting. I hunt East and West TX and drive this thing atleast 150 miles one way to each, usually a hunting weekend is 650 miles plus and then some hard wheeling getting in and out of these places.

    I checked into a gear swap and the cheapest i've found is $1200 for both axles and that is not fixing any problems with any leaking seals etc. This is not something I want to do myself.

    To everyone else, I really appreciate the info. I like and prefer to do things myself and it takes me a little longer than your average but I've done all of the work myself (sometimes that scares the sh!t out of me) but I know how to fix things when/if I break down.
     
  14. CyberSniper

    CyberSniper 1/2 ton status Premium Member

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    Since you're from Texas and a great many CK5 members are from Texas you should be able to find a set of 3.73 or 4.10 geared half ton axles for cheap. I know when I went from 2.73s to 3.42s it was cheaper to buy axles (even though it turned out to be about equal after so many replacement parts) than to regear. I wanted 3.42s because in the wintertime I run 235 rubber.
     
  15. dirtwarrior17

    dirtwarrior17 Banned

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    Agreed....sort of.

    No OD and 4.56's = bad gas mileage.

    carbs make sense if you want to make power on a budget.
     
  16. ntx78k5

    ntx78k5 1/2 ton status

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    That does make sense, I will start looking for axles and compare costs. The 342's kill me up hill and it wont hold a speed over 65. Once I break 65 and hit a hill or head wind its all she wrote. Can tow anything either.

    So 373's will let me keep my all around mileage and still be good in the slop and trails. No rock crawling here. Dont have the budget for it.
     
  17. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    WHat burt meant to say was "sequential fire injection" as a pose to "batch fire injection" is better, because the injector will only be firing when that cylinders intake valve is opening.. not the whole bank of 4 or 8 injectors firing all at once!
    Reguardless, MPFI (multi port fuel injection) is the way to go.

    I went from running a carb for 5 years to Tuned Port Injection. if you were on a budget you should be able to do the swap for $1K or less.
    (see k5 specs in sig) I picked up probably a mile to the gallon or two. Not huge, but noticeable.
    And i was amazed how it had more torque, horsepower, throttle response, and i picked up some mpg! :bow: :laugh:
    However, if you look at the bigger picture, if your engine is tired to begin with and needs replacing sooner than later, you could probably find an GenIII smallblock LS1 4.8/5.3/5.7/6.0 from a 98 up chevy, for around $1-3K. and find a low mileage engine with the sequential fire injection, get it all in one shot. :whistle:
     

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