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  1. #1

    Default Trans Swap For Better fuel economy

    Hi everyone, I did some searching, and I guess i didnt find the information im looking for.
    I have a 1989 suburban R2500 2WD, 454, 400 turbo trans. My gas mileage is crap at around 9mpg. i understand this isn't by any stretch a fuel friendly vehicle, but i was wondering whats my best path to save some money on fuel.
    I don't use it for towing large loads, usually just a few motorcycles to Daytona from Michigan once a year.
    My thoughts were; Trans swap to a 700R4, After market overdrive, or rear end swap. Any help will be much appreciated.

    Thanks in advance

  2. #2


    Changing all your fluids over to AMSOIL synthetic lubricants will more than likely give you 5% or more in your fuel economy. One of my neighbors picked up 2mpg just changing her engine oil in her 2008 Silverado with the 5.3L (20 to 22mpg). Do your engine oil, diff's, transfer case, and transmission. I can get you signed up as a Preffered Customer so you can buy at wholesale if this interests you.

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  3. #3
    Legend unplugged's Avatar
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    Sep 2006
    High Deserts of SoCal

    Thumbs up Hypermiling Z06 Vette averages 25mpg

    I think that 12 -14mpg is doable. The question is how do you want to get there and how much money do you want to spend? Slippery lubricants are a great idea and they don't penalize your wallet. A more efficient transmission is a good idea, but can run at least $1k - $3k depending on which trans you choose and whether you diy or pay someone else.

    I think the cheapest way to extend your mileage is to change the way you drive. Hipermilers use many techniques to double, even triple the normal mileage. If you adopted just a few of the tips a 5mpg increase wouldn't be out of the question without costing a dime.

    Read about the ins/outs of Hypermiling at:

    Here is the story of a Hypermiling contest in which a Z06 Vette averaged 25.77mpg.


    Driver Wins Fuel Economy Contest In A 505-Horsepower Corvette

    Think you’ve gotta drive a boring econobox or a hybrid to get decent fuel economy? Nope. A British moto-journalist took top honors in a fuel-economy challenge behind the wheel of a — get this — Corvette Z06 with a monstrous 7-liter engine.
    Journalist Richard Hammond (no, not that Richard Hammond) took hypermiling to a new level during the two-day, 411-mile MPG Marathon, achieving an impressive 30.96 miles per Imperial gallon (that’s 25.77 U.S. mpg). Although that was well short of the 84.66 mpIg (70.48 U.S. mpg) reached by the guy in a Toyota Yaris, it was enough for a win.
    There is no way to happiness....happiness is the way.:yipi:  _vXMYypuKMJFw671uF2ZPhjez_j-atRmcjM2zQKpQi1JSsB75/burb1.JPG
    High Desert SoCal
    93 K1500 burb (personal) 350 AT 3" Lift 250K+
    02 Honda Civic LX
    Looking for a 1990's Miata for an engine swap

  4. #4


    hypermiling might be tough with a trailer in the mountains, when we are trying to get there fast. But i'll definitely try some of those tricks. Ideally, I'm interested in in getting overdrive or something similar.

  5. #5


    Quote Originally Posted by dandizzo View Post
    hypermiling might be tough with a trailer in the mountains, when we are trying to get there fast. But i'll definitely try some of those tricks. Ideally, I'm interested in in getting overdrive or something similar.
    You can get bolt on overdrive units, this would be the best bet, all you'll need to do is have your drive shaft shortened becuae they bolt to the back of your tranny. However, since you have a 2wd, maybe you can get away with a 4wd drive shaft from the junk yard since the overdirve might be similar dimensions to a transfer case which would also have bolted to the back fo the tranny.

    sorry I don't have a link or a company name, but try googling "bolt on overdrive"

  6. #6


    A 700R4 will give you an overdrive gear that will help get some MPGs back. If you do all the work yourself, it should swap in with minimal changes and cost about $800 for a rebuilt transmission from a rebuilder, including core charges.

    1991 Chevy Suburban 1/2 ton 2WD w/ chevy SBC 350-3/4 ton drivetrain upgrade w/4.10 gears 200K miles
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  7. #7


    Gear Vendors make overdrive units for just about any car and truck. My dad and I put one on our old C30 with the 454 and the 4-speed. It was very pricey though (Looking at over $3k total), but my dad said it was worth it. I was too young to drive when he put it in (sold the truck before I could drive), but it gave us at least a 2 to 3 mpg gain on the city and highway.

    Here's the link to the units that should fit your 'burb, if you were interested:
    Last edited by bigburb; 10-23-2009 at 04:27 PM.
    Current truck: 1996 Ford 250, 7.3 Powerstroke diesel. Dana 60 SAS, stage 1 160cc injectors, T500 High Pressure Oil Pump, TS 6-position chip, full 4" exhaust, intake, 285 Falken Rocky Mountain AT's, boost/EGT/trans temp pillar gauges, etc...

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