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  1. #1
    Jr. Mechanic
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    Washington State, the Dry Side ( Southeastern)
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    Default 86, 454 Strip Down???

    Hey, Question out there???? I have a 1986 suburban 3/4 ton 454 carb'd that is set up for "leaded" gas, high emissions, no "cat's" straight line exhaust. Factory built this way, my question is has anyone ever striped the exhaust pumps and all of the vacuum off and let it run fully carb'd with just vacuum advance? This truck has no overdrive, no O2, and little computer components.

    I love the beast for pulling my horse trailer, but would like to clean it up performance wise, maybe just maybe lighten the load at the gas pump!!

    Thanks for any help you can give
    Just Another Day in Paradise...

  2. #2

    Default

    Is this truck U.S. or Canadian?
    After 1977 there were no U.S. street legal vehicles built to run "leaded" fuel. In fact after 1982 leaded fuel was getting hard to find in most areas. Some Industrial and Heavy duty trucks were built without catalytic converters, but the engines were designed to use unleaded fuel.
    Removing the air injector pumps for street use is illegal, federal law.
    There's very little power to be gained on this engine by removing the system. If your looking for power and economy try smog legal headers, dual 3" pipes, a balance tube, a better air filter and ducting system to draw air from outside the engine compartment, and an MSD distributer. Short of rebuilding the engine this is about all you can do. There were some replacement carbs made for this application but their expensive and usually give good performance but bad mpg.

  3. #3
    Jr. Mechanic
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    Jul 2007
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    Default

    TBplus.....

    Yes this a US Suburban.....And in fact the owners manual states that it is a High Emissions Vehicle. No cat's and it does have straight dual 3" pipes. It has the large fuel opening for the leaded gas,in the fuel door, I use lead substitute with the unleaded gas. The air cleaner does pull air out front of the radiator support. This has dual air pumps. No real help, on MPG.......not ever short of power.

    Thanks for the feed back!!!
    Just Another Day in Paradise...

  4. #4
    Legend

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    Jun 2006
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    River Ridge Louisiana-4 miles W of New Orleans-didn't flood-water stopped 800 yards away.
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    Default Leaded gas-probably don't need the lead substitute-small carb?

    You probably don't need the lead substitute.The vehicle must have been set up to run on leaded or unleaded.I'm sure it has the hardened valve seats that unleaded gas requires.There wouldn't be any point in building it without the hardened parts.Of course, if your owners manual says it needs a lead substitute.....I'm wrong.
    If you have a pile of money you could put an aftermarket ELECTRONIC fuel injection on it; I think Edelbrock,and probably Holly make a system for it.This probably would increase your mpg,and maybe the performance.I think they are expensive-$1500 or so-so it really isn't practical.
    Same story on trying to cobble together later GM FI and graft in on.
    One cheap idea would be to find the smallest 4 barrel carb you can-used-and put it on.With small primaries it might improve throttle response and MPG a little.It will kill peak power,of course, but who uses peak power very often?
    Luck,
    Charlie

  5. #5
    Jr. Mechanic
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    Default

    Charile,

    Thanks for that heads-up....the owners manual states leaded gas....I put the substitute figuring that it did not have the hardened seats....However you might me correct.

    With only 121k miles she is strong. The carb idea might work, but the lose of needed power when pulling might be too soft??

    Good Thought ...thanks
    Just Another Day in Paradise...

  6. #6
    Legend

    Join Date
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    River Ridge Louisiana-4 miles W of New Orleans-didn't flood-water stopped 800 yards away.
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    Default Hardened seats-late 70's I think- Do you have high compression?

    DJ Friction,
    I'm pretty sure you got the hardened seats.It would have cost GM more to make it without hardened seats,so they wouldn't have any reason to use unhardened seats. I think they called the hardened alloy-"stellite"-or something like that. I had to look this up years ago because I had a bunch of late 70's motorcycles,and they were leaded gas motors, but could use unleaded because the japanese had switched over by the late 70's.
    L
    Hey, have you checked to see when GM offered those monsters with TBI? My understanding is that the TBI is much less computer controlled than the later FI.They-the TBI were designed to fit non FI motors,so a TBI and its manifold might bolt on..You might get away with just a mass air sensor in the airbox snorkle,and maybe a O2 sensor in the exhaust. They would send a signal to the Electronic control,it sends a signal to the TBI.
    Might be fun to try, but $$ wise-even with junkyard prices-you could never make the $ back in saved gas.
    Thanks,
    Charlie
    PS I wonder if you got a higher compression motor also?
    I bet the real reason behind the "leaded gas" was to save the price of the cat con-they were expensive back then.GM and the commercial buyers/farmers might have convinced the EPA that they needed occasional leaded gas to lube the valve stems or rings in hard commercial use.It was probably BS,and a way to make cheaper vehicles with lower maintenance costs. Leaded gas did kill spark plugs kinda early-3000-5000 miles-, but they are cheap.

  7. #7
    Jr. Mechanic
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    Default

    Charile...

    compression....may have been higher, now just about 10:1, I think the best thing is the carb idea, I'm loking into that possible change.

    Thanks for the idea's

    Ken
    Just Another Day in Paradise...

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