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75 blazer guzles gas

Discussion in 'The Garage' started by gm guy, May 1, 2004.

  1. gm guy

    gm guy 1/2 ton status

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    OK, I have a 75 blazer with a 400 sbc and it runs great. My problem is I like to drive this truck allot but I can't aford the gas. I have changed motors before, so I can do this myself. Any idea's or opinions? I never realy liked the 305's but maybe a fuel injected one would be better. Should I go with a 305 or a 4.3 motor? /forums/images/graemlins/confused.gif
     
  2. beater_k20

    beater_k20 Banned

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    what are some of the specifics of your truck? gears, tire size, trans, case. im going to assume you're still running a Quadrajet. do not even consider the 305 or 4.3, less power produced by the engine means that the engine will have to work harder, and get worse fuel milage.
     
  3. gm guy

    gm guy 1/2 ton status

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    It's got a th350 4.10 gears and 35 inch radials. I think a tpi 350 could be the way to go.
     
  4. gm guy

    gm guy 1/2 ton status

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    Anyone have any highway mpg numbers for a tpi 350 in a blazer? I drive a ton to and from work!
     
  5. justinf

    justinf 1/2 ton status

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    I would say your best bet, rather than changing motors is to swap in an overdrive tranny to get better fuel mileage.
     
  6. Z3PR

    Z3PR Banned

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    Lets see, 4 wheel drive truck and crappy gas mileage ??? It's a cross we have to bear, but it's worth it in my opinion !!! Build the truck for power and forget the MPGs. For MPGs, get a cheap econobox little car. /forums/images/graemlins/whistling.gif
     
  7. gm guy

    gm guy 1/2 ton status

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    I see your point and I'm not expecting 30 mpg I just want 15 mpg. I don't want a pos 4 banger, but I think that tpi could make the difference I want. My 400 sbc is old and tired, thats probly half of my problem.
     
  8. bigyellowjimmy

    bigyellowjimmy 1/2 ton status

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    I think a 700R4 tranny would help more than anything for extended higway driving. Also a good carb tune-up. /forums/images/graemlins/thumb.gif
     
  9. gm guy

    gm guy 1/2 ton status

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    Yeah I'll give the 400 a second chance with a good tune up and a carb rebuild. Then if that works out I'll just swap in the 700 R4. Thanks for the tips.
     
  10. bigyellowjimmy

    bigyellowjimmy 1/2 ton status

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    Good luck /forums/images/graemlins/thumb.gif
     
  11. gravdigr

    gravdigr 1/2 ton status

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    [ QUOTE ]
    I just want 15 mpg

    [/ QUOTE ]

    ah hahahahaha
    /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif
    /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif
    snort, laugh, snort
    *wipes tears from eyes*

    I'd love to get 10MPG from either of my gas chugging pig blazers. Usually hovers between 5 and 8 depending on how I drive. PA mountains are hell on gas milage. I have been tempted to snag a sub $1,000 used civic that gets 30MPG for my long trips where the blazer isn't required.
     
  12. Z3PR

    Z3PR Banned

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    [ QUOTE ]
    I see your point and I'm not expecting 30 mpg I just want 15 mpg. I don't want a pos 4 banger, but I think that tpi could make the difference I want. My 400 sbc is old and tired, thats probly half of my problem.

    [/ QUOTE ] I would rebuild the 400sbc and convert it to TBI befor going to a 350. I love the torque my 400sbc has over a 350.
     
  13. supersize75k5

    supersize75k5 OrganDonorRacing.com

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    get a 4 speed or overdrive tranny, and a fresh 350, add the propper gearing, a new quadrajet and some profeshinal tuning on a dyno..walla /forums/images/graemlins/grin.gif
     
  14. gm guy

    gm guy 1/2 ton status

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    Thanks, I'll update you guys whenI get something done!
     
  15. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I get 16+ mpg from my Jimmy with 5" of lift and 39.5" TSL's, 4 speed and 4.56 gears. Of course the 6.2 diesel is a lot more efficient than a small block /forums/images/graemlins/grin.gif A smaller truck with a 6.2 and an overdrive can easily break 20 mpg using the 6.2.

    I can easily afford to drive mine daily, so I do. /forums/images/graemlins/waytogo.gif

    For comparison my old 350 was netting me 9 mpg on the freeway before. /forums/images/graemlins/yikes.gif

    So you can have your cake and eat it too...

    Rene
     
  16. 4xcrazy

    4xcrazy 3/4 ton status

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    11-13 on the highway, about 10 or so around town depending on how heavy my foot is. /forums/images/graemlins/doah.gif
     
  17. gm guy

    gm guy 1/2 ton status

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    The feel of a fullsized truck is well worth the extra money for gas. I won't be another 4 banger S-10 driver, but I do want better milage. I think a trans swap and a rebuild on the motor should help, also 3.73's instead of the 4.10's. Any tips on a fuel injection conversion? There are a ton of fi 350's around for parts. Is the 400 intake manifold different from a 350? Again thanks for the input. /forums/images/graemlins/k5.gif
     
  18. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    [ QUOTE ]
    Is the 400 intake manifold different from a 350?

    [/ QUOTE ]

    No it is not. All small block intakes will physically bolt on to each other from the begining of time ( to Chevy guys thats 1955 ) to the vortec era. When TBI and TPI came out in the 80's, the center intake bolts were angled differently, but can be made to work as the front and rear holes were the same, so its just redrilling the center ones . /forums/images/graemlins/k5.gif
     
  19. jarheadk5

    jarheadk5 1/2 ton status

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    [ QUOTE ]
    ...also 3.73's instead of the 4.10's.

    [/ QUOTE ]

    If you're running 35's and plan on sticking with them, DO NOT swap your 4.10's out. What little gain you may get at highway speed will be wiped out (and then some) as soon as you have to accelerate from a stop (which we all know happens fairly often...) Plus, you'd be going the wrong way when it comes to offroad performance.
    If you want to stick with an automatic, find a late 80's/early 90's 700R4/4L60 from a 4wd truck (I THINK '92 is the cutoff for the non-computer-controlled ones; if I'm wrong someone will point it out), get a quality rebuild done on it, and install it with a big trans cooler. This will probably net you the biggest mileage gain you'll see. Converting to FI will probably net some mileage too, but not as much as the OD trans (unless your carb is WAY out of tune). If your motor is tired, a rebuild will probably help, too.

    FYI, my '87 with a tired TBI305, 700R4, 3.73's and 33" AT's gets about 14mpg on flat, open highway. As soon as hills or traffic come into play on that highway, it'll drop to about 11-12mpg. Stop-n-go urban driving is 9-10mpg.
     
  20. kennyw

    kennyw N9PHW Premium Member

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    [ QUOTE ]
    also 3.73's instead of the 4.10's

    [/ QUOTE ]

    STOP RIGHT THERE. With 35" tires you dont want to step down to 3.73 gears. It will actually hurt MPG due to the extra strain.

    I get 14-15 MPG out of my '79 Chevy 3/4 ton 4x4 running stock springs, 285/75R16 tires (about 33"), 4.10 gears, a tired 350 and a 4 spd SM465.

    If you want to improve the economy you might want to step down to 33" tires and stock springs (or possibly down to a 2" lift) then swap out your tranny for either a 4 spd or 700R4 (auto/OD would probably help the most for MPG). Or if you want to keep the 35" tires regear to 4.56 and swap in the 700R4. Dont make the gearing higher, it only makes your motor work harder because it wont be running in its torque peak where it is most efficient.
     

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