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how improve mpg on 454

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by spincast375, Oct 3, 2004.

  1. spincast375

    spincast375 1/2 ton status

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    I bought it with a rebuilt 454, 1000 miles. Many of the carburetor's connections have been plugged or cut (fast idle, vacuum). Mpg is awful at seven highway and maybe eleven city. A fellow 4x4-er said it has a newer carb (std Chevy, not Holley or Edelbrock), and many of the pollution devices didn't exist on older engines. This doesn't sound right. Any suggestions on the kind of shop I should take it to, and questions I should ask? I can maintain what I've got, but when it comes to missing parts, I am lost.

    The only 4x4 shop in middle TN does well on suspensions, etc. But I didn't see any tune-up equipment in the bays.
     
  2. Bruiser

    Bruiser 1/2 ton status

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    hmm don't know what you are after , do you have a overdrive tranny and what are your gears? 7 and 11 sounds great for a big block, I am lucky to get 10 out of my smallblock in my blazer. I can get 18 out of my camaro but it has 2.56's in the rear :P
     
  3. spincast375

    spincast375 1/2 ton status

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    Transmission is standard TH350, yes, with overdrive. Gears are 3.73 front and rear. I could understand the low mpg if she had great acceleration. But she is pretty much a dog.
     
  4. Rolled

    Rolled 1/2 ton status

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    [ QUOTE ]
    Transmission is standard TH350, yes, with overdrive. Gears are 3.73 front and rear. I could understand the low mpg if she had great acceleration. But she is pretty much a dog.

    [/ QUOTE ]

    TH350 does not have overdrive... I agree with the above post, 7/11 is great milage for a Big Block. I get 10 in my k5 /forums/images/graemlins/eek.gif
     
  5. Bruiser

    Bruiser 1/2 ton status

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    Rolled is correct a TH350 isn't a overdrive tranny, you would have to have a 700r4 to be an overdrive. What size are your tires? With 3.73's shouldn't be much of a dog unless your tires are huge. But sounds like there are some other issues. You may find that once you make it not be a dog your mileage will go down since then you will be on it more. What type of carburator is it, intake, exhaust system? Try tuning the carb correctly and see what happens. Can be done easily with hand tools and a vacuum guage. If don't know how let us know I can find the link or someone where will to show you how to tune the carb.
     
  6. k20

    k20 3/4 ton status

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    The 3.73's are what are killing your in town mileage. You are running 35's, im runnin 4.10's and 35's on my 496 (of course im fuel injected) and I get 10-11 everywhere. Your highway mileage is high (relatively) because of those high gears (w/ or w/out OD since trans is unknown) therefore keeping your rpm's down. But in town, it is a dog, high gears, so have to put your foot in it to get movin, suckin down the gas). If you have 35's and do in fact have OD, go 4.56 gears. If dont have OD, 4.10's would be a better bet. If you plan on bigger tires, gear it a little lower.

    O yeh, to identify your trans, Look at the pan. If it looks like a square w/ a corner cut off, its a th350, if it looks like a square, a 700r-4(has OD), and if it looks vaguely like indiana, its a th400
     
  7. spincast375

    spincast375 1/2 ton status

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    Thanks for the comments, looks like I am struck. Anybody want to swap at 454 for a 350 before I go broke? Gas is $ 189.9 here.
     
  8. SF87K5

    SF87K5 1/2 ton status

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    where are you located?
     
  9. k20

    k20 3/4 ton status

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    well, honestly, even ditchin the 454 you aint gonna pick up much(if any) mileage. With my old tree fiddy i got 8-10. Most people w/ perfectly tuned 350's only get 12-14. I would guess gears would be the best you could do right now, for mileage and power. Did you figure out what trans you have?
     
  10. 84gmcjimmy

    84gmcjimmy 1 ton status

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    where do you live?
     
  11. justhorsinaround

    justhorsinaround 3/4 ton status

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    We used to have gas that only cost a buck ninety. It's up to 2.15 most gas stations round these parts for mid grade. /forums/images/graemlins/yikes.gif
     
  12. J.R.

    J.R. Guest

    i will make that trade! /forums/images/graemlins/peace.gif
     
  13. spincast375

    spincast375 1/2 ton status

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    I am just south of Nashville, TN.
     
  14. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    If you want mileage swap a 6.2 into it with a 700R-4 and some 4.56's. That combo should net you 20-22 mpg.

    Either that or buy a 4 or 6 cylinder car...

    Rene
     
  15. ratzila

    ratzila 1/2 ton status

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    I bought a toyota 4x4 xcab for my dd. /forums/images/graemlins/rotfl.gif When I swapped a 454 into my burb it actually got better mpg than the old tired 350 /forums/images/graemlins/woot.gif:There is nothing better other than swapping in a diesel if you want better mpg.
     
  16. sickquad

    sickquad 1/2 ton status

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    If you really want it to run well you need to have it put on a chassis dyno and tuned. I get my bike tuned every spring, it's amazing. A couple of my friends have gotten there drag cars done also.

    -Chris
     
  17. airheadpilot

    airheadpilot Registered Member

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    I have a 1987 3/4-ton 4x4 Suburban with a brand new crate 350 and all stock intake (TBI) and exhaust. TH350 tranny, stock tires. I have good acceleration and get 12-14 pretty consistently.
     
  18. cegusman

    cegusman 3/4 ton status

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    I have a 6.2 diesel I will swap for the 454 /forums/images/graemlins/dunno.gif
     
  19. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Thats text book perfect MPG. Thats the same as I get with my FI 88 454 Burb. Only way you are going to make it any better is Over drive and then you might get 14. OD is $2k

    Course if you drive a lot and don't need the truck most of the time a $1000 bomb that gets 30 mpg is the hot ticket. Our Burb is parked except for when we all need to go somewhere or we need to tow. $1000 89 Honda Accord gets 31 mpg and paid for itself in fuel savings in 4 months. When it blows the motor in a couple years I will wad it up throw it away and buy another and have a low milage Burb in the drive way to drive while I find the next $1,000 bomb. /forums/images/graemlins/thinking.gif
     
  20. dremu

    dremu Officious Thread Derailer Premium Member

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    Grim's on the right track; even with insurance and registratration, another car can save you $$ quick.

    I'm down to five cars after I moved out -- my wife kept the other ... umm, three or four.

    A car for every purpose, if not a purpose for every car. I have a Nissan and an Isuzu for day-to-day stuff ... a /forums/images/graemlins/k5.gif for topless fun ... a Chalet for camping ... and a /forums/images/graemlins/crewcab.gif six-pack for moving more people and/or stuff than anything else will fit /forums/images/graemlins/laugh.gif

    Of course, mileage goes down with each... but I don't drive the big-block /forums/images/graemlins/crewcab.gif every day. (Actually, it's getting better mileage than my /forums/images/graemlins/k5.gif ... and they're both '74's with Quadrajets ... that Blazer needs looove, I tell ya.)

    -- A
     

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