Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Gear Ratio a problem?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by firemanparamedic, Mar 8, 2007.

  1. firemanparamedic

    firemanparamedic Registered Member

    Joined:
    Jun 28, 2006
    Posts:
    7
    Likes Received:
    0
    Location:
    Houston
    Hey guys Im pretty new here and just wanted to run this by you. I have a 91 K2500 Ext Cab Long bed, its got a 350V8 with a 3spd tranny (sorry dont know the name of the tranny) . I bought this truck a little over a year ago, an it is basically just for pulling my boat (18ft aluminum boat its a duracraft so its actually almost as heavy as a fiberglass boat). My only complaint thus far is that my gas mileage is less than dismal. A visit to the local 4x4 shop, an I was told that I needed to change out my gears (my truck has 4.10)to a higher gear, get a K&N air filter installed and put a chip in. My first question: would changing my gears out improve my gas mileage that much? Second question what about the Air Filter and Chip....I love this truck, and want to keep it, so is a chip a good idea (hurt the engine?). Third and last question: My truck has a granny gear and Im thinking thats a transmission thing and that changing my gears wont effect that, is this correct? Thanks alot guys.
     
  2. 1977k5

    1977k5 3/4 ton status Vendor

    Joined:
    May 26, 2003
    Posts:
    9,992
    Likes Received:
    130
    If you have a 3 speed in an automatic then you have a TH400. It definitely doesn't have a granny gear, in fact it has the highest 1st gear ratio of all of Chevy's autos.

    Gears are not going to help your mileage. You are towing with a gas motor, poor mileage is part of the game. The K&N filter and chip will not noticeably change mileage either.

    The best thing you can do to help mileage is make sure your truck is well maintained. Check spark plugs and wires, distributor cap and rotor, fuel filter, and maybe run some injector cleaner through it.
     
  3. imiceman44

    imiceman44 1 ton status

    Joined:
    Aug 5, 2002
    Posts:
    15,160
    Likes Received:
    1
    Location:
    Sacramento, CA
    Like he said the gas motor will not get you good mileage, the higher gear ratio might actually hurt you because then the engine will be pulling hard instead of pulling comfortably with the 4.10
    The filter is a good addition but don't count on seing the difference in the mileage, you might feel it a little more peppy but that is all.
    the chip won't hurt, it might free up some of the ponies hiding in there but again no noticable difference in mileage.
    Are you getting any less than 9 MPG?
    That should be the worst with you 91 and the setup you have.
    Should get about 13-14MPG empty too.
     
  4. firemanparamedic

    firemanparamedic Registered Member

    Joined:
    Jun 28, 2006
    Posts:
    7
    Likes Received:
    0
    Location:
    Houston
    Gear ratio replys

    Im getting around 9mpg towing, and about 13mpg empty like you said. As far as the tranny goes, its a Manual with a low gear, 1st,Second,and 3rd. Id call that a 3spd with a granny but mabye some call it a 4spd. Thats kinda what I thought about the gears and towing, doesnt make sense that raising my gears would improve my mileage towing. Another bit advice Ive gotten from the local shop was to raise my truck and put bigger tires on...to improve gas mileage....but Im thinking the increased friction from a larger tire will just hurt my mileage anymore. Thanks for the responses sorry it took so long to get back..she broke down on me and been spending my days in the garage.
     
  5. imiceman44

    imiceman44 1 ton status

    Joined:
    Aug 5, 2002
    Posts:
    15,160
    Likes Received:
    1
    Location:
    Sacramento, CA
    OK with a 4spd as we call it, or more precisely a manual tranny, you can get away with some things you can't with auto.
    You could swap for taller gears or one size bigger tires and you might pick up 1 mile per gallon on the flats, but don't expect miracles on the hills.
    The trick to get the best mileage is to keep the engine in it's sweet zone.
    Some people think getting it to stay in the highest gear will get them the most but if you down shift to keep the engine pulling without revving it too high which is where the fuel dumps in the throttle body, then you can get better mileage.

    I don't know where the sweet spot on a 350 gasser is but if you can learn that and keep the engine there when you drive long distances that is where you will see the mileage go up.
    I did that with my diesel and got 30MPG but if I don't watch it, doing the same load I can get as low as 20MPG.
    :o
     
  6. 6.2Blazer

    6.2Blazer 1/2 ton status

    Joined:
    Feb 24, 2000
    Posts:
    4,675
    Likes Received:
    26
    Location:
    Ohio
    You did not mention what size tires you have, but if they are fairly close to stock size then the combination of 4.10's and no OD in the tranny isn't the best combination for fuel mileage when empty. And depending on the weight of the boat (I'm guessing not a huge number) then it may not be optimal for towing either.
     

Share This Page