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Headers w/ a cat. convert?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by woodpecker, Oct 20, 2000.

  1. woodpecker

    woodpecker Registered Member

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    Well, I'm still waiting on the money to rebuild or replace my carb (loose throttle shaft), but am still daydreaming about future mods.

    I live in a county that is exempt from emissions crap, but still have a concern. My '86 Blazer has a cat/convert and I want to know if this is bi-passable. Does an engine this modern have a computer that would be totally thrown off?

    Will I have to run headers into a cat/convert and out one pipe? Anyone who's put headers and dual exhaust on an '86 or newer blazer, I'd love to hear from you.

    woodpecker
     
  2. BurbinOR

    BurbinOR 3/4 ton status

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    I believe the computer controlled FI motors began in '87, so don't think there is a computer on your's. The other guys reading will surely speak up if this isn't the case. The engine wouldn't be thrown off anyway, as the O2 sensor is sampling the exhaust mixture BEFORE the catalytic. Guys put headers on computer controlled motors all the time (so am I, with theoretically a '92 TPI ECM on my '79 406 now) with no issues. I hear the newer vehicles have the "big brother" OBD2 version of the computer software and hardware that has 2 O2 sensors that take readings before the cat AND after the cat, but in your case shouldn't matter.

    <font color=black>'79 - 406 TPI -<font color=orange> K5#5 - <font color=blue>See it at---&gt;http://www.blazzinor.coloradok5.com
     
  3. blazen91

    blazen91 1/2 ton status

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    To conferm: 86 and back was carbed., 87 and up was FI'ed.

    blazen91
     
  4. FWP

    FWP CRS

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    Alright, time to put in my 2 cents. Many of you won't like my reply, but it's just my opinion. Emmisions equipment does not hurt (yes, there is a few exceptions) a damn thing. Especially with the new stuff. Catalytics DO NOT reduce flow (unless it's from the 70's, or you're runnin a 10,000 RPM race motor). Anybody who lives in LA, Phoenix, Albuquerque, can attest to the fact that smog is not a good thing. Trying to reduce this in a responsible manner is good for everyone. I'm not talkin about race vehicles, show trucks, or any off-road only stuff. Pulling off emmisions equipment in the attempt to gain something on a daily driver does not make sense. Many benefits are gained from running a clean machine, eg. You know when you have some engine performance problems when the emissions go up, You are not the target for environmentalist wackos (Algore), you reduce the risk of the government passing legislation in your area to implement mandatory testing, and you can say that you are doing your best to keep the area you live in clean. I'll get off the soap box now. Thank you.

    <font color=blue>Maverick</font color=blue> <font color=red>CH 4 or 35</font color=red>
     
  5. Chrome Moly

    Chrome Moly Registered Member

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    O.K Gents I'm setting the record straight. I have a 88 350 tbi, headers, straight pipes, glasspaks. And hate to say,
    but my computer is (confussed) meaning with no back-pressure my Idle is around 2000 RPM!!!! My chip is set from the factory to run with a cat, and with no cat means no back-pressure, and with shory block style headers I have
    a fire breathing 350, and to my limited knowledge the only way to bring the idle down to normal is either get a new chip, or have someone reprogram your current chip, or put cats back on. Autozone has cats for $64.00 I'm gonna
    get two tomarrow and bolt them on.

    Chrome Moly
    <font color=green>Resistance is Futile</font color=green> [​IMG]
     
  6. AJMBLAZER

    AJMBLAZER Better to be lucky than good. Premium Member

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    Do like I did. Have a good local exhaust place fab you up a system with high flow cats and Flowmasters. I'm in SoCal, and no one here will make a dual exhaust (even though my truck isn't registered in Cali), but I will have duals made after I get out of the Marines and go back to Michigan for a while. A good high flow aftermarket cat won't cost much more than a stock replacement cat, they flow just as good or better than stock (although some argue this point), and the exhaust tone smoothes out. I am glad I got mine, not to mention you have to have a cat there if there was one there from the factory, by FEDERAL LAW! So I will run one (two when I get dual put on) just to keep any actually legal and automobile cops happy. Most don't care just as long as you have a cat or two there. It doesn't hurt anything anyways.

    1992 Blazer Sport, 350 TBI, 4L60, 3" Flowmaster, K&N, 3" Rancho, 285/75R16 on 16x8 Baja's[​IMG]
     
  7. Chewy

    Chewy 1/2 ton status

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    BlazzinOR is right. The computer engines don't start until 87, however the O2 sensor is ahead of the cats so it doesn't matter. I am running true dual exhaust (with cats) on my 87 and there are no problems. By the way, dual exhaust sounds way meaner than single pipe. Just my opinion.[​IMG]

    [​IMG] '87 Beast
    Colorado, USA
     
  8. 87Blzr

    87Blzr 1/2 ton status

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    My 87 is going to get duals with headers and dual cats. If you go to a performance exhaust shop they probably have a bunch of cat take offs you can get cheap ( a friend says a local shop near him has a 55 gal. drum filled with new Mustang cats that people wanted cut off and new exhausts put on.) I am going to see if I can get a couple cheap. Cats don't hurt flow, especially newer ones. Also, TBI started in 87, not computers. Computers have been around since the early eighties and earlier, carb or FI. Woodpecker, you have a computer.

    87 K5 Siverado, 68 SS 396 Camaro
     

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