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Changing ratios for better MPG

Discussion in 'Chevy C/K Truck Forum' started by pino55, Oct 5, 2010.

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  1. pino55

    pino55 New Member

    How do i find out what I have and what would is compatible to switch to? Has anyone done this? I'm doing a few things to try and improve my fuel efficiency. Thanks.

    '88 silverado k1500
    5.7 tbi
  2. silveradotrailblazer

    silveradotrailblazer Epic Member 5+ Years ROTM Winner 5000 Posts

    Look in your clove box for the codes. GT4=3.73, GT5=4.10, GU5=3.23, Gu6=3.42. You will have to change both front and rear gears sets. Sometimes just putting a taller tire on the truck, not to tall will help with MPG's because it changes the gear ratio.
  3. KWG08VMI

    KWG08VMI Rockstar 100 Posts

    you can look up the RPO codes and determine what the factory put in, they are located in the glove box. Or you can jack the rear end up and count tire rotation vs. drive shaft rotation. As for what's compatible, you can get pretty much any ratio you want. The question is what size tires do you have. That will determine what ratio you should go with. If you have stock tire size you may be able to drop a ratio, say from a 3.73:1 to a 3.42:1 or if you have upgraded then maybe from a 3.73:1 to a set of 4.10:1's
  4. silveradotrailblazer

    silveradotrailblazer Epic Member 5+ Years ROTM Winner 5000 Posts

    It's expensive to change gears. I would try other things first like switching all the fluids (engine,transmission, transfer case and front & rear axles) to synthetics' clean your fuel system including removing the throttlebody and cleaning with throttlebody cleaner, not carb cleaner, fuel filter, cap & rotor, wires, spark plug (run the factory A/C Delco's) and air fliter. If you use a fuel system cleaner (Seafoam works great) do it before you change your oil.
  5. pino55

    pino55 New Member

    I have just finished doing the cap, rotor, plugs(always the delcos), wires , fuel filter , oil. Since it's and older truck should i worry about the synthetics causing any leaks?? I heard that can happen. Going to also get a new air intake and headers to help the MPG's. Anything else??
  6. silveradotrailblazer

    silveradotrailblazer Epic Member 5+ Years ROTM Winner 5000 Posts

    The new synthetics work with older engines, years ago they would leak in the older engines but not now. Just clean the fuel system and the throttlebody.
  7. 2COR517

    2COR517 Epic Member 5+ Years 1000 Posts

    Excellent post.

    Good quality tires (Michelin) with a mild highway tread will also yield an economy improvement.

    What size/type tires do you have now? Lift kit?

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