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Thread: Highway gears?

  1. #1
    Registered User pr1mo360's Avatar
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    Highway gears?

    hey guys, im planning a long trip (2,000 miles). I was thinking about changing my gearing. I heard 2.5 s10s have low gear ratio called highway gears.. How much fuel do they actually save? also could i swap out my overdrive gear or get another trans that would drop the revs low at 70-75?
    i gotta 85 2.8 auto btw

  2. #2
    LQ4/LS1 Turner's Avatar
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    cant change the overdrive gear in your tranny and you done want it any lower then around a .7:1 ratio anyways. as far as rear diff gears go a 4:10 wil give you good launch off the line but a higher rpm at highway speeds, a 2:72 gear ratio will give you horrible off the line speed but much lower rpm on the highway resulting in better fuel mileage. but the cost of swaping gear ratios would not be worth if your just going on a couple long drives, if your going to use the vehicle for alot of highway driving then it might pay out in the long run. hope that helps.

  3. #3
    Registered User pr1mo360's Avatar
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    i can get parts from pick n pull for practically nothing and i really dont care about off the line performance. i just want the rpms really low at 70-75.
    is there a way i can calculate how much fuel i will save with the rear end gears? also will i get better mileage on the highway with bigger or smaller tires?

  4. #4
    LQ4/LS1 Turner's Avatar
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    i would not recomend putting in a used gear set, if your going to do it, do it right and buy new stuff. and if you are going to be installing it you need to know how to set your preloads, backlash and tooth pattern.

  5. #5
    Your mom's box! slammins15's Avatar
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    Check the rpo codes for your truck if you already have say 3.08's you not gonna save much by putting in a lower gear ratio like 2.72's It would take LOTS of driving to make up the fuel savings vs cost of gearing swaps. Swapping gears in a diff isn't just as simple as throwing them in and tightening the bolts you kninda have to know what you are doing or they won't last a block. If you're gonna do it buy a complete used diff and install the whole thing.
    Last edited by slammins15; 02-03-2010 at 12:57 AM.
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  6. #6
    Registered User pr1mo360's Avatar
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    yeah i would get the whole rear end.
    ill be driving betweeen Reno,Vegas,OC and Texas a few times a year. i already have the blaze all stripped down as much as i could. no ac or power steering,efan... dropped 6/7 with 215/70/15. i really want to get smaller tires but i figure it would hurt highway mileage?
    i plan on swapping in a 2.2 or 2.5 with a manual trans but for now i wanna try to get 25mpg at 70mph with my current setup. If i can get the gearing so the rpms super low like 6 gear on a c5, i can play with timing and carb adjustment to get everything i can out of my 20 gallon tank. Sometimes i need to make it like 200 miles to the next petrol station. its freaky when your in the middle of the desert low on fuel

  7. #7
    LQ4/LS1 Turner's Avatar
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    with my tbi 4.3 in my truck i get 22 mpg in the city and around 28-30 ish on the highway. got e-fans, syn. oils, throttle body spacer, and e 3 plugs. in my opinion for all the work needed to change everything its not worth it. if you want fuel economy buy a little civic or something lol.

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    I agree with Turner. With all the work/$ your gonna put into your Blazer to get any kind of good gas mileage you may as well just get a little honda.

  9. #9
    Registered User pr1mo360's Avatar
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    i can handle the work and parts are cheap,trust me i know my way around a blazer
    i do have a tacoma that gets 32 mpg. but its to uncomfortable for long trips. im gonna have some stuff with me and i love my blazer for road trips.

  10. #10
    Registered User Myself's Avatar
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    I would guess you probably have 3:42 gears with that eng/trans combo. 3:23 or 3:08 would help with the mileage and still work ok on the low end with that overdrive. Have you done the simple stuff already? A k&n type air filter, a tune up with good quality plugs, switching to synthetic oil, and upgrading to a multiple spark ignition system will all help the mileage out too.

  11. #11
    Zombie Killer 6SpeedBlazer's Avatar
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    Quote Originally Posted by Turner View Post
    with my tbi 4.3 in my truck i get 22 mpg in the city and around 28-30 ish on the highway. got e-fans, syn. oils, throttle body spacer, and e 3 plugs. in my opinion for all the work needed to change everything its not worth it. if you want fuel economy buy a little civic or something lol.
    im gonna call BS on this.

    there is no way that e-fan synthetic oils and a tbi spacer get you ~10mpg over what the factory rates them at for fuel mileage.

    my 4.3/t56 combo didnt not even get that good of mileage. the best i was able to get with it was 27mpg on a trip out to kansas

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    I'd have to agree with 6speed on this one.

  13. #13
    LQ4/LS1 Turner's Avatar
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    well i have no reason to lie about my fuel mileage, i was just posting a fact. and thats not 10 mpg over factory as my stock winter jimmy that is the same drivetrain as my red blazer gets 17 mpg in the city, so 22mpg with a few upgrades in city is very possible.

  14. #14
    Zombie Killer 6SpeedBlazer's Avatar
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    the only way i could see it being even remotely true is if he is referring to Imperial MPG instead of US mpg.

    28-30ish would translate to 23-25ish

  15. #15
    Zombie Killer 6SpeedBlazer's Avatar
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    Quote Originally Posted by Turner View Post
    well i have no reason to lie about my fuel mileage, i was just posting a fact. and thats not 10 mpg over factory as my stock winter jimmy that is the same drivetrain as my red blazer gets 17 mpg in the city, so 22mpg with a few upgrades in city is very possible.
    you stated 30mpg highway.

    stock they are rated at 18-20 highway depending on how they are optioned out.

    thats ~10mpg more.

    edit now that i think about it i would bet that your speedo/odometer is just way off from something.
    Last edited by 6SpeedBlazer; 02-17-2010 at 08:10 PM.

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