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Cat. after the muffler?

Discussion in 'The Garage' started by 88K5Jimmy, Jan 3, 2006.

  1. 88K5Jimmy

    88K5Jimmy 1/2 ton status

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    My exhaust:

    2.25 out of both sides. Driver side into a 3". Passenger side y's behind the t-case into the 3" on the driver side. 3" single in and out of 40 series delta flow. I got the factory cat cut off after I lifted it and had all the exhaust work done. I am thinking about putting a high flow cat back on in order to eliminate some of the resonance inside the cab. However, to only get away with one cat and not have to get another tailpipe made, there is a spot after the muffler that is long enough for one of these high flow cats to go.

    http://coloradok5.com/forums/showthread.php?t=159860

    http://www.performance-curve.com/index.asp?PageAction=VIEWPROD&ProdID=1060&HS=1

    So would there be problems with the cat going after the muffler, i.e. more resonance, choking up, loss of muffler noise all together?

    Thanks
     
  2. sandawgk5

    sandawgk5 3/4 ton status

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    The cat will not get hot enough being that far down the exhaust that it will not burn of the bad stuff and it will clog and hinder your performance.

    Ira
     
  3. 88K5Jimmy

    88K5Jimmy 1/2 ton status

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    What if I put it where the muffler is now, which is in the stock location? Basically after the passenger side y's back in.
     
  4. sandawgk5

    sandawgk5 3/4 ton status

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    I am not sure. There is a heat shield under the drivers side floorboard. That is where the cat should go as designed by GM. Will it work 1 foot aft of that ? Maybe no way of telling what the exhaust temp will be at that point also your engine might run warmer than factory depending on what mods you have done. Generally it is best to put it where it belongs.

    Ira
     
  5. 88K5Jimmy

    88K5Jimmy 1/2 ton status

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    Hmm..that would mean I would only have the driver side with a cat on it. Wonder what that would do....
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    See if you can find the article by David Vizard about power and exhaust.

    It's a pretty interesting read, I believe he covers resonance.
     
  7. 88K5Jimmy

    88K5Jimmy 1/2 ton status

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    I couldn't find that article but I did find a post on here about backpressure and pipe sizes. It said that enlarging your pipe size will decrease your low end torque. However, I haven't increased it anymore than it was stock. Due to how my exhaust is run I wonder if putting a high flow cat back on, located a little farther forward than the location where the muffler goes will net me any low end torque back, or is that too far downstream in the exhaust? I know it will probably take some of the resonance out of the exhaust, which is what I want but it won't be as quiet as if the stock cat was still on there.
     
  8. 6.2Blazer

    6.2Blazer 1/2 ton status

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    It would filter 1/2 of the total exhaust. In any case not something I would recommend.

    Regarding the pipe size vs. low-end torque, don't get your hopes up that it will do much unless you really have the pipes mis-sized for your engine. Sure, if you put dual 4" pipes on a stock 350 you might lose some low-end power because the pipes are simply to big to effectively scavenge the exhaust gases, and going back down to dual 2.25 or 2.5" pipes would help. In general the whole idea about pipe size vs. backpressure vs. low-end torque has really been blown out of proportion. I don't think putting a new style converter will make much of difference considering they are designed to be as free flowing as possible.
     
  9. 88K5Jimmy

    88K5Jimmy 1/2 ton status

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    Yeah I wasn't expecting a miracle or anything. My exhaust right now is comprised of 3" and 2.25" so it's stock, so to speak on a stock 350. I remember when I had my same exhaust setup only with the stock cat and after I had the cat cut off it got a lot louder inside. So that's why I think a high flow cat would take care of some of the resonance but not completely take it back down to the level it was at with the stock cat and current exhaust setup. I just wonder if the placement is really a big deal in regards to exhaust resonance. I don't have to worry about passing a sniffer test in this state.
     
  10. 6.2Blazer

    6.2Blazer 1/2 ton status

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    If you are simply concerned about interior resonance and sound, then I think you should simply look at getting a different muffler. That option sounds a lot simpler than trying to splice in a converter.
     

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