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Thread: Fatshotzs drastic HP loss

  1. #1
    Join Date
    Aug 2017
    Location
    USA
    Posts
    1

    Default Fatshotzs drastic HP loss

    HI, I have a 91 FLHS, with a new carb model S&S 96 and Baker 6 speed installed last fall. I have a true dual head pipe setup, with Radii 3.5 inch slip-on with 2.25 inch baffle ( Rhinehart Knockoffs ) in it. It was dyno-tuned 2 months ago running 89 hp and 99 ft torque. Too loud, I installed the 4 inch Fatshotzs slip-on with 9 discs. Had the sound and quietness I was looking for. Started with 9 discs but lost a lot of performance. Installed all 12 discs and a little better, but still a dog. Took it in to be dyno-tuned, with the closed end cap and 12 discs. 1st pass the HP dropped to almost 40 hp. Dyno guy took off all discs and closed end cap. HP back to 75 HP range, and had some snap again. I would prefer to use the closed end cap for noise reduction. Any suggestions on how many discs to add. I just installed 12 discs with the open end caps and back to louder than what I wanted. I would prefer to use the closed end cap. Reading a lot of forum posts they have adding up to 18-22 discs on each muffler, but that seems to be with the 2 into 1 setup. I will be bringing it in to be dynoed again. Any help, Thanks.

  2. #2
    Join Date
    Jul 2007
    Posts
    387

    Default

    Quote Originally Posted by microdot View Post
    HI, I have a 91 FLHS, with a new carb model S&S 96 and Baker 6 speed installed last fall. I have a true dual head pipe setup, with Radii 3.5 inch slip-on with 2.25 inch baffle ( Rhinehart Knockoffs ) in it. It was dyno-tuned 2 months ago running 89 hp and 99 ft torque. Too loud, I installed the 4 inch Fatshotzs slip-on with 9 discs. Had the sound and quietness I was looking for. Started with 9 discs but lost a lot of performance. Installed all 12 discs and a little better, but still a dog. Took it in to be dyno-tuned, with the closed end cap and 12 discs. 1st pass the HP dropped to almost 40 hp. Dyno guy took off all discs and closed end cap. HP back to 75 HP range, and had some snap again. I would prefer to use the closed end cap for noise reduction. Any suggestions on how many discs to add. I just installed 12 discs with the open end caps and back to louder than what I wanted. I would prefer to use the closed end cap. Reading a lot of forum posts they have adding up to 18-22 discs on each muffler, but that seems to be with the 2 into 1 setup. I will be bringing it in to be dynoed again. Any help, Thanks.
    Sorry for the late response, was in Sturgis for the last few weeks.
    My first thought would be that the discs are overtightened? It's easy to do. 12 discs should be flowing way more than enough for that motor.
    Check that the dscs are not too tight. Those mofflers have 2" cores, also more than enough for that motor, you should see better torque numbers as well.

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