Alternative Fuel Conversions for 1976 Suburban (454) ? [Expired Topic]

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by Lesechang, Jun 24, 2006.

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  1. Lesechang

    Lesechang New Member

    Hello. I live in Tucson, Arizona, and drive a gasoline-powered '76 Suburban with the big block (454) engine. Having kept meticulous fuel records since October, 1996, when I inherited the beast, I find that I have been averaging 9.33 miles per gallon and have driven over 91,000 miles. I know how to change the oil and spark plugs but can do very little else. I am not a mechanic - not even in my dreams!

    I have heard of Suburban conversion kits for CNG, LP, and biodiesel (doesn't apply in my case). I have also heard of computer chips that replace distributors for increased power & mileage.

    Fuel costs $2.69 per gallon today (June 24, 2006), but I'm sure it will hit $3.50 per gallon or more in the near future. There are gas stations here which sell E85, but they charge almost as much as regular gasoline! The website reports that E85 sells for $2.65/gal today, which is only four cents less than gasoline, hardly worth the cost of conversion!

    QUESTION: given the above info concerning my specific Suburban, what realistic alternative fuel conversion options are available?

  2. Davandy

    Davandy Moderator 5+ Years ROTM Winner 1000 Posts

    The best alternative is LPG Propane. but you have a little les power and you have to find a place to put the gas tank. :wink:
  3. 84fiero123

    84fiero123 Epic Member 5+ Years 1000 Posts Platinum Contributor

    Sorry or should I say glad to say you truck has no computer so that option is out.

    If you do not tow with it you can try changing the rear end for a more fuel efficient gearing. With a motor that size you are going to be hard pressed to get much better mileage no matter what you do short of changing motors or the rear end.

    You do have the ultimate tow vehicle tho. With the 3 ton + truck and the monster motor there isn’t anything you can’t tow.

    Hell I wouldn’t worry what I wanted to tow with that it can handle it and that is what it was made for.
  4. OldDiesel

    OldDiesel Rockstar 100 Posts

    Yup, computers didn't start appearing in cars and trucks until about 1980 or so.

    As far as the fuel economy goes, is your truck a 2 or 4 barrel motor? I imagine it's a 4, but if not, swap out the carb and manifold for a 4 barrel. Believe it or not, as long as you keep your foot out of the secondaries, it'll improve your milage. With that engine, you should have either 4:11 or 4:56 gears. If you don't tow much, or at all, change the gears out in favor of 3:55 or 3:27s. The biggest thing you can do (and cheaper than an alternative fuel swap kit) is an overdrive tranny. Look into Gearvendors overdrive units. I'm sure they make a kit to retrofit into your application. You could also swap the trans completely, in favor of a 200r4, or with a little more work, a 700r4 or 4L60. Overdrive is your friend. I would expect that if you swapped the gears for a 3:55, and swap the old three speed you've got (should be a th400 in your truck, but might be a th350) for a more modern 4 speed, you could be in the middle to high teens milage wise.
  5. Lesechang

    Lesechang New Member

    Thank you all for your input.

    I have a rebuilt carburetor that cost about $200, so it isn't the fancy one.

    The engine has never undergone a major overhaul, but the transmission was rebuilt/worked on about ten years ago, and I remember hearing the words "turbomatic" and 400 (or was it 4000?). The mechanic noticed that the passing gear wasn't hooked up, so he fixed it.

    How much would it cost to regear the beast and replace the transmission?

    All my friends tell me to chuck the Suburban and buy a smaller vehicle.

    NO WAY!

    Tucson is growing exponentially, and with it, bad drivers from all over the US and Mexico! I feel safe in the Suburban. If I get into an accident, the odds are that the other guy will be in the hospital and I'll be scratching my head wondering if I ran over a squirrel. Also, you can't beat this Suburban for visibility. There are almost no blind spots with the large left and right side mirrors. My friend in NM says that I should stop complaining about the low mpgs and just consider it cheap life insurance.

    Still, getting 15 mpg would be amazing, or even miraculous.
  6. ChevyFan

    ChevyFan The Sheriff Staff Member 5+ Years 1000 Posts

    I've spent a little bit of time in Tuscon, very pretty town. :)
  7. OldDiesel

    OldDiesel Rockstar 100 Posts

    Changing the rear gears shouldn't be too expensive, probably $300-$600 depending on the gearset and who does the install. The trans, well... That's a little more.
  8. Lesechang

    Lesechang New Member

    I like Texas, too!

    Lemme run this by you all.

    A friend here in Tucson says that I should swap out my stock carburetor for a comp cam 252 duration (Townsends Racing Works) and get a 500cfm 2 barrel carb. He also says I should disconnect the passing gear. He's done this to his other chevys and got much better mileage and better performance! He says I could be getting 13-14 mpg with my 454 monster.

    What say You?
  9. 84fiero123

    84fiero123 Epic Member 5+ Years 1000 Posts Platinum Contributor

    Go with the 4 barrel like old diesel said the primarys are smaller than on the 2 barrel and then when you need the extra juice you still have it.
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