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Headers and dual exhaust

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BLzr4x4ngkid, Mar 12, 2000.

  1. BLzr4x4ngkid

    BLzr4x4ngkid 1/2 ton status

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    I want to put headers and dual exhaust on my jimmy. what would be the best headers and exhaust system to use, but at a reasonable cost? i don't want to spend a fortune on just exhaust, so let me know. thanks

    alex

    "What me get stuck? NEVER!!"(Famous last words)
     
  2. Chris Demartini

    Chris Demartini 1/2 ton status

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    <font color=blue>Well, you have an 87 so it's TBI. A "true" dual exhaust (one where there is a seperate pipe for the odd and even cylinders and they never connect) would cause computer and emissions problems, but you can come close. I've never seen a short-length header for a K5 blazer, but an exhaust shop could probably build up an ehuast using full-length emissions headers and then make a Y-Pipe to conect them to to the cat. A high-flow catalytic converter would help lots too. Then, build a cat-back with a flowmaster muffler. I found a single 3" in, dual 2 1/2" out Flowmaster 40 series direct replacement for a suburban in http://www.jegs.com, and that would be a good muffler. Then have an exhaust shop biuld you tailpipes out to the sides or back of the truck. this would be cheaper than a Flowmaster cat-back because it is fully aluminized, and therefor, more money. Of course, after all this you need to get the air in fast before you can get it out fast, so a K&N filter is a good idea. You just need a 14"x2" round element for the stock air cleaner. A chip might also be necasary to help the computer cope with all the increased airflow. My freind just picked up an 87 this week, so we'll be doing an exuast soon.
    Hope this helps</font color=blue>
     
  3. NJ SAR Guy

    NJ SAR Guy Registered Member

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    Okay, I think the only thing in your message that was correct was that an 87 is TBI.
    A "True" dual exhaust will not screw up the computer on a TBI system. It's done all the time. As long as you keep an O2 sensor in the header.
    Every company that makes headers (that I know of) makes shorty headers for Blazers and Chevy Trucks. Hooker, Headman, Schoonfield, Edelbrock, Summit. Don't know about Dynomax, but I'd be willing to bet that they have 'em too.
    As for The flowmastr and the high flow cat, yes that's a good idea. Better flowing exhaust will give more power. But I believe that too little restriction will kill your low end torque and will only give you more power higher up in the RPM band.
    As for the K&N air filter, I have this to say about it:

    "As for the K&N filter, they will make claims as to 3-5 HP inprovment and torque improvements.
    Maybe.
    Personaly I think the power increas is actually a fraction of a horsepower, but even if it is 3-4 HP, you probably won't even feel the diffrence.
    But...
    Even though it's no big power increase, I LOVE K&N filters. I think it's the #1 thing that EVERYONE should put in their car or truck if they care about it. Not because of power, but because it's just a better filter. And it'll pay for itself eventually since it's reusable. Just a god investment. Kind of like using better oil. It won't realy make you faster, or give you more pulling power. But it's beter for your engine."

    Now that my standard genaric speach about K&N filters is out of the way, let me say this.
    They are NOT that high flowing that they would EVER require a new chip to cope with the higher airflow. I WISH!
    Look, I'm not trying to be mean or anything, but I think you should realy pick up a good book and learn a little bit more about computer control systems. I drive an 88 myself, my friend has a 92 Camaro with true Dual Exhausts (and dual cats). Basicly the same TBI small block motor that I have in my 88, or BLzr4x4ngkid's 87. It runs fine and passes NJ emmissions (now the same as CA emmissions, I believe) just fine. I have a K&N filter. So do all my friends that don't just drive beaters. They never needed anything done to their ECMs or PCMs. Not trying to bash you, but these are realy minor, standard modifications that any properly running computer should be able to cope with without modification.
    Hope this clears things up a bit.


    NJ SAR Guy

    Please excuse all of my misspelled wurds.
     
  4. Zack

    Zack 1/2 ton status

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    Correct me if I am wrong BUT:
    During TBI operation the computer updates itself by using a a/f table. Once you get on it it automatically goes into a special mode that uses preset a/f mixtures. Its been a long time since I have read up on this stuff but I believe this to be true. So you wouldn't need any new chips to compensate for the exhaust or filter. If its giving you fits when you do do that then just unhook the battery and reconnect it to reset the computer. Then it will be forced to give you a table of mixtures. I would think the K&N would help more on carbed engines cause there is no computer to compensate for it. Just my opinion I could be wrong. Send all flames to Screwyou@sorryaboutthemistake.com

    Zack Carlson




    No I am still not done with my frame up resto!! Soon i swear!
     
  5. Sledge

    Sledge Registered Member

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    You are right in that TBI is a "speed-density" setup. It has a grid of vacuum vs RPM and has injector pulse-widths at each point in the map. But it also has what I think GM calls a "block-learn" mode, where they kind of tweak the table a bit over time. I think it's meant to help compensate for changes in engine efficiency (like compression loss) over time. It's not a very aggressive change though. A buddy and I scratch-built a FI setup for his Austin-Healey racecar and you can really create a fast ramping change, but it can cause oscillations and some nasty little problems. I'm pretty sure that's why GM took just the slight tweak.
     

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