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73-87 Big Block shorty headers?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Shawn, Mar 22, 2000.

  1. Shawn

    Shawn 1/2 ton status Premium Member Author

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    Does anyone make big block shorty style headers for the 73-87 trucks? The closest I found was Gibson but they listed it for a mid-late 90's with a 454. You would think these would fit in an older truck but I hate to take chances.

    I was also thinking about running a single 4" exhaust with my 454. Any idea where I can get the 4" SS mandrel tubing?

    Thanks in advance.

    Shawn
    87 K5
    454
     
  2. jmpd

    jmpd 1/2 ton status

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    Why would you go from duals to single. Is it for looks? Where will it exit? out the back, side, behind the tire??

    In AZ, Loper's Performance has almost everything you could need---sometimes. 602-264-5288 no web site
     
  3. Shawn

    Shawn 1/2 ton status Premium Member Author

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    I have to mount a single o2 sensor in a place where the headers join so a large single would be ideal and should be the same (if not more) in power. I was going to route the single exhaust behind the rear tire. I'm not concerned with looks, just functional. Right now my duals mount under my rear bumper which result in exhaust fumes coming in the rear window if open. Thanks for the info!

    Shawn
     
  4. Mudzer

    Mudzer 1/2 ton status Author

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    Shawn, I may do the same. My Bro can build Flowmaster type mufflers and I am going to have him build one (4") for me. All stainless of course. I am checking right now on tubing. I will have a shop install it. I was planning on 3" crossover then 4" after that. I need to install an O2 senser bung because I am planning a future FI install. Anybody need some Alumanized 2 1/2" exhaust for a Blazer with Dynomax mufflers??? Contact me.

    <font color=red>Mudzer</font color=red>
    1978/91 K5 Blazer
     
  5. jmpd

    jmpd 1/2 ton status

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    Shawn,
    What are you running now? Are they full length headers? What size collector?
    Where is your o2 sensor now?
    What size tubing before muffler and what size after muffler?
    What type of muffler? 2 or 3 chamber flowmaster?

    I read the profile of your truck, but can't remember what you said you were running. How much Horsepower ETC.

    The reason I'm asking is because I 've been around my buddies in the exhaust biz for awhile, and that sound a little different.

    Because you are going from duals, muffs, cats and exist pipes to a smaller or same size exhaust.

    Just wondering. But opinions are like a**holes
    Good luck
     
  6. Shawn

    Shawn 1/2 ton status Premium Member Author

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    Right now I'm running Dynomax ceramic headers with 3" collector and they are full length headers. There is no o2 sensor mounted now since I'm running a carb but I just purchased a Holley MPI system so I'm trying to think ahead. I'm running 2.5" tubing with the 2.5" (in/out)flowmasters but I'm not sure about the chambers. I don't run any cats (shhh). My HP at sealevel should be around 425. Here in Denver, it's less.

    The reason for a possible power increase is this. If I add an "H" pipe to my duals, it will increase power right? This creates a balance between the 2 pipes and has been proven on the dynos. A single large exhaust does the same thing. Plus my 2.5" pipes are bent poorly and it looks like they go down to 1.75" in some areas. The mandrel bent tubing will always be 4". I'm also planning on running a 4" muffler which Flowmaster makes.

    Another thing about my existing longer headers is they run too close to the thicker ORD front shackles and front driveshaft. When off-road, these are going to hit.

    If anyone else has comments about this, I'd like to hear them. I'm no exhaust pro but this sounds the most logical to me.

    Shawn
    87 K5
    454
     
  7. Blazer79

    Blazer79 1/2 ton status

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    Shawn:

    If the only reason you're changing everything is the O2 sensor, I think you could be fine installing it right after one of the headers. The computer will adjust all the mixture depending on the feedback the O2 sensor gives. If the O2 sensor senses lean when installed on one side, it means the other side is lean as well (unless there is something really wrong with your intake manifold), therefore affecting the other side too. The computer will then adjust for a richer mixture. My brother's Camaro has the O2 sensor mounted in one of the exhaust manifolds.

    Does the manual mention anything going wrong if not installed that way? I think it's just to get a more 'average' reading of the mixture.

    <font color=purple>////////
    Drive it like gas is </font color=purple><font color=red>$2.00/gal!!!</font color=red>
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  8. Shawn

    Shawn 1/2 ton status Premium Member Author

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    I'm not just doing this for the o2 sensor. My headers come too close to my shackles so I have to replace my headers. I was told by few good sources that the o2 sensor should be mounted where it senses both sides. If it wasn't for the clearance problem, I'd do that but since I have to replace the headers and re-do the exhaust, I might as well install it between the 2.

    Just for the hell of it, I dug up a geometry book, blew the dust off it (and cleared the cob webs out of my head). Anyway here's some figures that you might find interesting:

    Area of a circle = pie*radius(squared)

    area of 2.5"= 4.908" (total of two 2.5" pipes = 9.816)

    area of 3"= 7.068"

    area of 4"= 12.566"

    So you can see that even two 2.5" tubes will flow less then then one 4" This means a 4"exhaust should give you more HP in the upper RPM but the torque might drop a little at the lower RPM range.

    Please correct me if I'm wrong on this.

    Shawn
     
  9. AZK5

    AZK5 1/2 ton status

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    My 86' Suburban with 406 sm blk TPI has the O2 sensor after one of the headers with dual exhaust. Everyone in the fuel injection industry that I called said that wouldn't be a problem and that most aftermarket setups are that way. On my K5 I tried to increase the torque of the motor but keep it in the lower rpm range. Big exhaust increases upper rpm power, but decreases low rpm torque. Tell us how it turns out. Big truck and bus repair shops should be able to fab up 4" exhaust for you.
    CB
     
  10. jmpd

    jmpd 1/2 ton status

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    Hey, I talked to my buddy at the mufflershop he said, he would just mount a single bung on the header collector or right after collector and into new pipe for the o2 sensor. He said he did'nt see the advantage of a single 4". He said with that much horsepower 400+ he would run 3" to 3.5" duals. He said that all you would have to do is have then ends of your existing mufflers opened up to 3" or 3.5". That is the only difference in Flowmaster is the in and out. If your happy with the current mufflers just open them up to accept the larger pipe.

    I hope this helps. Not sure on the Shorty Headers?

    good luck
     
  11. Blazer79

    Blazer79 1/2 ton status

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    For simplicity's sake, why don't you run dual 2.5"? That's what I'm using in mine (it's a 350, though). I think you'll have a hard time finding someone who bends 4" pipes (I couldn't even find someone who bends 3" pipes). Besides, I'm not sure if the 4" pipe can clear everything in the way, especially the transfer case area. You'll only need that extra size if you are running very high rpms, and since it's a Blazer, I don't think you do.

    Another pain in the a$$ is making a 4" Y-pipe. I think it's much easier to run smaller diameter duals. I installed an H-pipe right after the T-case, (because there was no space before it). I'm very happy with the whole system (Flowtech afterburners, O2 sensor installed in one of the reducers, two Flowmaster 40 series, and the H-pipe).

    <font color=purple>////////
    Drive it like gas is </font color=purple><font color=red>$2.00/gal!!!</font color=red>
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  12. Shawn

    Shawn 1/2 ton status Premium Member Author

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    Thanks for the comments guys. I was only trying to go with the single 4" since it seemed cheaper (only 1 SS muffler) and I do have plenty of room to route it. It acutally seems easier to run 1 large pipe then 2 small ones.


    Regards,
    Shawn
     
  13. jarheadk5

    jarheadk5 1/2 ton status

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    This is interesting, because I was planning on running a single 3" system. I had read in a Four Wheeler back issue that a 3" single is better for low-end than a 2.5" dual (with or without H-pipe) due to the exhaust pulses blending (or not blending, I forget which). Less tubing to buy & have bent, too. Anyone else confused, or did I read it wrong??

    [​IMG] Semper Maintenance!
    [​IMG] So many ideas, so little money...
     

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