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gas mileage

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by wheelnut46, Dec 14, 2001.

  1. wheelnut46

    wheelnut46 1/2 ton status

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    I just bought this ’77 GMC Jimmy from a neighbor and checked the gas mileage. It is all stock with a 350, 4 bbl, TH350 and 95,000 miles. The hubs have been converted to warn locking hubs. It has 31 inch tires. It is my daily back and forth to work and to my sons school driver. I seem to only be getting 10 MPG. I know its not going to be very good on gas so I have been really trying to baby it. I have a built TH350 that I was going to use in the ’46 Chevy pickup, but I’m thinking of putting in the blazer with an RV torque converter. I was also thinking of taller but skinnier tires if there are any but not right away. What other ideas do you guys have to improve gas mileage?

    '77 GMC Jimmy
     
  2. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Increase the gear ratios. If your truck has low ratios (2.73 [​IMG], 3.08, or 3.48), you may want to get 3.73s or even 4.10s. The idea behind this is that you will make it easier for the vehicle to accelerate. My truck gets the worst mileage in town (stop and go)... but once its at 65mph on the HW, my mileage goes up to ~11mpg.

    I have a 454, which in town only gets about 6MPG[​IMG][​IMG]. I also have 36" TSLs, which killed the mileage compared to the 35x12.5 BFG ATs I used to have.

    Get her tuned up real good, and put a 195 stat in her too. The higher stat equals better mileage too. [​IMG] Pull the AC if at has AC - and you dont need it of course!!!

    Other than that - there isnt much. These trucks were never supposed to get good mileage, even though some folks will tell tales of K5s that get 16MPG.... But I call BS on that!!!!

    Just my .02...

    <font color=red>GOT MUD???</font color=red>
    My license plate reads:<font color=blue> 8 YR SUV</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s - 36" TSLs
     
  3. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    One more idea... go and get yourself a subscription to 4WOR magazine! They have a monthly column on how to improve mileage on our beasts...

    <font color=red>GOT MUD???</font color=red>
    My license plate reads:<font color=blue> 8 YR SUV</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s - 36" TSLs
     
  4. hammer

    hammer 1/2 ton status

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    6 cylinder j/k That's all I get 10-13 mpg on the highway and I have OD that I can't use with 32" and 2.73 gears.

    <font color=red>Let me at it I can break it</font color=red>
     
  5. CaptCrunch

    CaptCrunch 1/2 ton status

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    Well I guess first off... if you want milage, the balzer is the wrong way to go. It isn't gonne be likely to get mmuch more then 15. Also you really need to look at a number of items. #1 like was said gear ratio? #2 I recomend a complete tune up, msd coil, and gap the plugs over .060. New fuel filter, check the timing and advance. #3 spoend a good amount of time learning to tune you carb. I have gotten 15 mpg with a very similar combo. but it did have a lockup style converter which I don't believe yours has. Not sure what year they started doing lockup th350's... 82 maybe?

    -Mikey
    1987 Chevy K5 Blazer- 350 TBI
    <a target="_blank" href=http://coloradok5.com/gallery/captcrunch>http://coloradok5.com/gallery/captcrunch</a>
     
  6. schwinnd

    schwinnd 1/2 ton status

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    I've got a '76 blazer with a 350/th350 and a non-converted 203 and I get about 10-11mpg around town and 12-13 on the highway. I've 3.73's and 31x10.50 at's. I'm just happy gas prices are dropping[​IMG]. That means I get more gas for my 20 bucks a week.

    Just collecting rusty mid-70's chevy's
    1976 Blazer, 1975 Vega SW
     
  7. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    You could swap in a 4 speed...that'll net 1 or 2 MPG increase. Cap'n Crunch had some good suggestions too. Make the motor run as efficiently as possible. Better ignition, a very tuned carb etc all help. Freer flowing exhaust also helps a bit.

    Aerodynamics are a big problem...as well as stupid gearing from the factory in a lot of cases. 3.08's will just make it lug...

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
    <a target="_blank" href=http://coloradok5.com/gallery/project_T2> tRusty pics...</a>
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    The freeway/city mileage is going to be very different in one of these trucks for the most part. (really high numeric gears typically give you low in both respects, but more even numbers)

    If those are freeway numbers, then you probably have a bit of a problem, or a few. One thing I would revert back to, if its aftermarket, is a quadrajet. Even a 600CFM is less efficient than a Q-jet while crusing.

    There are numerous LOOOONG posts about mileage here, might I suggest you do some searching?



    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>www.dorianyeager.com/index2.html</a>
    Why insist on counting when the ring gear has the tooth counts stamped in?
     
  9. rocko

    rocko 1/2 ton status

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    swap in a 700r.. .
    I'll keep my OD tranny anyday...
    As long as you maintain the 700.. their damn good trannies.
    I'm going to install a tranny cooler on both of mine..
    My 89 w/ 350tbi/700r/3.73gears I was getting about 18mpg being easy on the gas.. I'd get 390 to 410 miles per tank before doing the axle swap... that's when i was running 2.73's.

    I haven't failed, I've found 10,000 ways that don't work. www.rocko.rockcrawler.com
     
  10. jwduke

    jwduke 1/2 ton status

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    For what it would cost to swap in a manuel tranny, you would never make back enough to pay for the swap. As the earlier post said, I'd swap in a TH700R-4 from a '87 or later pickup, or you could increase your gear ratio to 3.73 &amp; that could gain you a mile or two. Chances are your Blazer has a 3.07 gear ratio. A lot of them did. Good luck!

    1 ton '87 Chevy SWB in the making!
     
  11. shoeless

    shoeless Registered Member

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    It will take a long time to break even after swapping to a 700 and adding gears. With my 700, 33inchers and 3.08 gears, I still only get around 13 mpg(highway).
    Probably the best thing you can do, is do a good tune-up and make sure your tires are aired all the way up. You'd be surprised at what a difference that can make.

    Oh yeah, and keep your right foot out of it.....

    Shoeless
    '88 K5
     
  12. wheelnut46

    wheelnut46 1/2 ton status

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    Yes, it does have the 3.07 gears. My 5 speed V6 powered Toyota 4-Runner with 4:11's gave me 16-18 MPG. I'd be out of my mind for 18 with the Jimmy. I'll settle for 15 though. I doubt that a good tune up will net me 50% increase in gas mileage. The 3.07 gears are good for the highway right? Actually most of my driving is around town. Are you saying that my plans for the Edelbrock dual plane and 1406 carb are not going to help?

    '77 GMC Jimmy
     
  13. Thunder

    Thunder 3/4 ton status

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    The 1406 carb wont help the milage any. I think you would be better off sticking with the Q-jet.
    You might be better served spending money on one of these:<a target="_blank" href=http://www.jetchip.com/fuel/streetmaster800.cfm> jet performance Q-jet</a>
    And doing what other posts sugested, complete tune up, dual exauhst, Ect
     
  14. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    I was really stoked to build up a 454+ cid big block for my blazer...
    But I'm afraid with the 6-8MPG city and 12-13MPG freeway I get with my current 355 engine in my '72 K/5... The extra weight of the big block, more cubes, bigger carb, etc. will only make my gas milage worse...
    (*SARCASTICALLY*)
    So I'm deciding to swap in either a straight six or something more like a 1.8L Honda 4 banger.
    What do you guys think?

    Blazers aren't fuel efficient cars, there big, Full Size, gas guzzlin', bad ass, trucks. Its a trade off.
    [REAL MEN DON"T CARE ABOUT GAS MILEAGE OR RAPID TIRE WEAR!]
    Ryan B.<P ID="edit"><FONT class="small">Edited by Ryan B. on 12/15/01 02:46 AM.</FONT></P>
     
  15. wheelnut46

    wheelnut46 1/2 ton status

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    Thats real encouraging - Thanks for the tip.

    '77 GMC Jimmy
     
  16. Danno

    Danno 1/2 ton status

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    If you want good mileage out of a K5, gotta have the diesel. Of course, I might be biased. Hehehehehe!

    The truck in my sig gets about 18mpg daily driving (mix of town and highway), and I've hit 27mpg on long trips a couple times. It's too bad diesel costs more than premium gas where I live. What a *$*#^@ RIP OFF!

    If you want good mileage out of your gasser, you're going to have to have a transmission with some kind of overdrive (700R4 auto, or NV4500 manual) and reasonable gearing/tires.

    And, as others have mentioned, keep the engine in tip top shape.

    1984 K5 Blazer 4x4 Silverado
    6.2L diesel, 700R4, 3.42 gears, 31x10.5" tires
     
  17. SlyDog

    SlyDog 1/2 ton status

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    Ryan, then according to your sig you aren't a real man [​IMG][​IMG]

    <font color=green>[​IMG]1977 K5 GETTIN IT AWN[​IMG]</font color=green>
    BUILT NOT BOUGHT
     
  18. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    See above post.
    Just to clarify.. I was being a smartass...
    Who in their right mind would put a 1.8L honda engine in a K/5!? You couldn't tell I was kidding? [​IMG]

    [REAL MEN DON"T CARE ABOUT GAS MILEAGE OR RAPID TIRE WEAR!]
    Ryan B.
     
  19. Ancient_4X4

    Ancient_4X4 Registered Member

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    10 mpg seems a bit low. Perhaps you need a more efficient carb. My 400 gets about 12 mpg, hell when it was new it got over 15 on a trip to Canada, according to my dad.
     
  20. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    I agree with Thunder - those Jet Q-Jets are great. Lotza folks report &gt; mileage &amp; performance. Too bad they hit you for $350-400 for one! [​IMG]

    Screw that! I'm going fuel injected in the spring... because RyanB is right about the 454 - the one in my truck eats me out of house and home! [​IMG] BUT, you know I love every minute of it!!!

    I think I should be able to pull 12MPG after the $1200 FI unit...

    <font color=red>GOT MUD???</font color=red>
    My license plate reads:<font color=blue> 8 YR SUV</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s - 36" TSLs
     

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