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Thread: After removing the cat

  1. #1
    Join Date
    May 2015
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    Default After removing the cat

    I have an 11 touring model and have removed the cat from the head pipe. I have the Harley Fatshotz with the ten plates and open end cap and with the cat removed the sound is louder. What is the best way to lower the noise? What would happen if I take five plates out of the right hand side and leave ten on the left since the left hand pipe only gets a portion of the exhaust in the first place?

  2. #2

    Default

    Quote Originally Posted by pettifogger1 View Post
    I have an 11 touring model and have removed the cat from the head pipe. I have the Harley Fatshotz with the ten plates and open end cap and with the cat removed the sound is louder. What is the best way to lower the noise? What would happen if I take five plates out of the right hand side and leave ten on the left since the left hand pipe only gets a portion of the exhaust in the first place?
    We would suggest the opposite of what you are saying. You have two options, you can use a closed end cap or you can run discs 5 discs/open end cap on the left side (clutch) and 8 discs/open end cap on the right side.

    You don't mention how the bike was running, only sound so you will have to determine the actual # of discs depending on if you want more bottom end power or top end power. Less discs more backpressure, more bottom end power and quieter. More discs louder, leaner and more top end power. But always more discs on the right side.
    Hope this helps!
    hugger@supertrapp.com

  3. #3
    Join Date
    May 2015
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    Default

    Thanks, it's actually a Trike so I am more interested in bottom end.

  4. #4
    seawoo Guest

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    I guess i am lost... Back in March i asked generally the same question..... I was told same amount in discs each side?? Which is correct?? Reference Fat Shots and PCV. Today i am running gutted cat, PCV, open end cap with 5 discs per side. Looks like the top of my header pipe (not shields) are turning blue.. Lean right? So should i reduce number of discs per side? How many??

  5. #5
    Join Date
    Aug 2008
    Location
    Blackfoot, ID
    Posts
    119

    Default Which is correct???

    The correct answer is for you to tune the diffusers yourself using SuperTrapp's procedure (taken from their FAQs):

    "The answer depends on your displacement: disc diameter, power band, and noise level, [as well as, your bike's modifications and atmospheric conditions (i.e. AMSL)]."

  6. #6
    bschultz Guest

    Default

    In the case of "true duals" the number of discs should be equal on both sides, my co-worker was thinking OEM headpipe (pre '09).

  7. #7
    Join Date
    May 2015
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    Default

    Took your original advice of 5 discs on the left and 8 on the right. Went down to 3 on the left and 5 on the right. Bike runs good and actually sounds pretty good. I would, however, like to see if I can lower the sound level just a bit. If I were to try some closed end caps, how many discs should I start with?

  8. #8
    bschultz Guest

    Default

    To keep the same exhaust flow/performance add 10 discs with the closed end cap in place of the open end cap.

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