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Mistral exhaust db killers

Discussion in 'V7/V85/V9 Chat & Tech' started by senecagreen, Dec 17, 2020.

  1. senecagreen

    senecagreen Tuned and Synch'ed

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    The V9 roamer I bought came with Mistral long mufflers. After reading about how some have db killers installed I looked at mine and there they were. I removed them to look at them and I bet they have been cut. I will post a couple of pics and maybe someone else that has them can say.

    I actually have a decibel meter (not a app on my phone) and I have checked all my bikes especially before changing exhausts to see the difference between stock and whatever I bought. Since I don't have stock V9 exhaust I checked the Mistrals with and without the db killers.

    With the db killers
    idle 81db
    cruise rpm 94db
    revved 108 db

    Without the db killers
    idle 83 db
    cruise rpm 94db
    revved 108 db

    I always set the meter 8ft away and directly behind to be consistent. Not much difference is why I think the previous owner modified the db killers.

    20201217_170712.jpg 20201217_170704.jpg
     
    Mayakovski likes this.
  2. vagrant

    vagrant GT Reference

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    look normal to me. if you run without them it's best to put the screw and nut back into the exhaust pipe or the empty hole will create a tweety bird noise.
     
  3. GTM®

    GTM® Administrator Staff Member GT di Razza Pura

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    Why not Google it? ;)
    Yes, they’ve likely been cut. Most all of them have an end cap with a hole drilled in it.
    3CA96199-43FC-4533-8C11-69925DDA331D.jpeg
     
  4. senecagreen

    senecagreen Tuned and Synch'ed

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    I dis google it but could not find the actual Mistral oem db killers. Just other aftermarket alternatives. If someone has a pic of the oem ones I could probably reconfigure mine as I know some excellent welders who could weld up whatever I make. You have probably figured out I like to make things which is why I admire your fabrication skills.
     
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  5. vagrant

    vagrant GT Reference

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    [​IMG]

    V7III shorties on the left V85 on right.
    I did buy the V7III set used so it's always possible the original owner did cut them. But, he didn't say he had and there was no sign of it and no soot or sign they had ever been in or run.
     
  6. jpv7

    jpv7 Cruisin' Guzzisti

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    my V7 mistral shorties have killers like what Todd posted, but without the hole.
     
  7. aproud1

    aproud1 Tuned and Synch'ed

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    Same here. Pretty big difference in vs. out. Pretty sure you can buy replacement stock baffles if you want to quiet it down. There is a small but noticeable power improvement with out the baffles.
     
  8. senecagreen

    senecagreen Tuned and Synch'ed

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    I can fix the ones I have then. Thank you for the info!
     
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  9. senecagreen

    senecagreen Tuned and Synch'ed

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    looking at the mg store website for db killers the ones I have look like the "loud" db killers for the california 1400 mufflers and not modified
     
  10. senecagreen

    senecagreen Tuned and Synch'ed

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    I wound up ordering the California 1400 db killers. They were too big to fit in my Mistrals but once cut they did slip over the ones I had and I was able to use them after all. Once installed I will check with my decibel meter the difference and post the results

    I was able to repurpose one of the ends I cut off to modify a db killer I had for a slip on on one of my other bikes.

    20201217_170704.jpg
    20201230_205116.jpg
     
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  11. senecagreen

    senecagreen Tuned and Synch'ed

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    Food for thought...I am not a sound engineer nor am I a air flow engineer. You notice I made them longer than oem length. I can still cut and weld them shorter to oem length but wanted to experiment.

    The muffler construction and anything you add like db killers are affecting 2 very different things. more/faster combustion explosions make more waves/vibrations that your ears turn into sound and the frequency of that sound determines bassy or harsh.

    Then you have to consider the engine is a air pump and needs optimum flow for the capacity.

    So the db killer configuration and location affects flow and sound. The muffler being either chambered or straight thru affects both too. Most of the slip ons you deal with are straight thru with either a louvered or perforated core. Resonator construction is interesting too.

    Air picks the path of least resistance. So by making the decibel killer longer moving the escape route further into the muffler and keeping in mind the mistral db killers have those extra little escape holes around the bell.

    I really was just curious how that would affect the air flow, noise level and frequency of the sound. Todd makes slip ons and puts a lot of thought into what he makes.

    I really don't know the science, I just enjoy thinking about all that goes into these things...
     
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  12. senecagreen

    senecagreen Tuned and Synch'ed

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    Got them in and checked them with the meter
    idle 81db
    cruise rpm 92
    revved 104 db

    Compared to my original open db killers
    idle 81
    cruise rpm. 94 db
    revved 108 db

    I think they still have plenty of flow and am happy with the result. Would they have been louder if I had made them shorter like oem? I don't know
     

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