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  1. #1

    Exhaust drone - 3inch K24a3 CL9

    Hi Guys,

    I've recently upgraded to a 3 inch cat back single exit exhaust and am currently chasing to remove a very loud drone between 2400 and 3500 rpm.
    It's especially bad when you stop accelerating, making around town driving anoying.

    Current exhaust setup is:
    Littlebo custom 4-2-1 headers
    High flow 2.5inch cat
    Reducer to 3 inch
    2 foot straight through hot dog resonator
    Then 3 inch all the way to 2.5 inch baffled muffler.

    The resonator and muffler are both redback exhaust branded.

    I have tried to the fix this drone by adding a Helmholtz resonator that is just before the muffler and angled towards the other exit.
    The length is roughly 370mm.

    It's helped to remove a lot of the deep bass notes, but it's still far from perfect. I had a friend on my car recently and they said it sounds like a truck, especially when you are on deaccleration.

    Any suggestions on what to do?

    I am planning on modifying the Helmholtz resonator to make it slightly longer at 430mm to see if this helps, using the below forumla.
    ((343)÷(3000×4×(1÷60)))÷4.
    The 3000 is my Rpm


    Sent from my Pixel XL using Tapatalk

  2. #2
    Member Array
    Join Date
    Oct 2004
    Location
    www.alibaba.com
    Car:
    porsche boxster
    You need a proper muffler in the middle not a hotdog. something like this


    also what kind of hiflo cat? 100cel? the biggest issue with my exhaust noise was the 100cel cat,it made the car unbearable compared to the oem cat with same catback setup

  3. #3
    I don't actually know the cel. I believe it's 100.
    What's funny though is that I've had the headers and the high flow cat installed with the stock catback for a couple months without any annoyance at all. It honestly sounded stock.

    I do have a 3 inch s bend muffler that I could probably try and put into the exhausts, but it's off centred so it's a littles annoying to install.

    Aren't the hot dog resenators meant to remove drone.

    Sent from my Pixel XL using Tapatalk

  4. #4
    Member Array
    Join Date
    Oct 2004
    Location
    www.alibaba.com
    Car:
    porsche boxster
    in my experience hotdogs remove raspiness not bass

  5. #5
    Quote Originally Posted by EKVTIR-T View Post
    in my experience hotdogs remove raspiness not bass
    I'll definitely keep this in mind. Might be a bit of a weekend job

    Sent from my Pixel XL using Tapatalk

  6. #6
    I extended the length of the Helmholtz resonator by 120mm and it seems to be quieter. Not by a lot, but a bit. I also added a hanger on the end of it as well now that it's longer which has dramatically improved the stability of the exhaust. Before on idle you could even hold it to stop it shaking. Now it site still just like the factory exhaust.

    So still worth modifying it, but still have drone. One day I'll have to get another resonator, bit for now it's driveable.

    See my Instagram post for some video clips.

    https://www.instagram.com/p/BeSdGIkBDJJ/

    Sent from my Pixel XL using Tapatalk

  7. #7
    Member Array
    Join Date
    Oct 2010
    Location
    Melb
    Car:
    '03 Euro [CL9]
    What is the size/diameter of the Helmoholtz resonator?

    i believe the "offsetting" effect of the Helmoholtz is reflected by the diameter itself compared to the pipe size.
    2003 CL9 5AT *ECU REFLASHED*
    CT-E Icebox|Ralco RZ pulleys|K&N filter|DC Header|250cell Cat|Cusco Tower & H Brace| H.Drive Coilovers | Rays RE30 18x8.5 | S/S Brakelines | Rigid Collars

  8. #8
    Quote Originally Posted by Fredoops View Post
    What is the size/diameter of the Helmoholtz resonator?

    i believe the "offsetting" effect of the Helmoholtz is reflected by the diameter itself compared to the pipe size.
    It's 3 inch. Same as the rest of the pipe

    Sent from my Pixel XL using Tapatalk

  9. #9
    Member Array
    Join Date
    Oct 2010
    Location
    Melb
    Car:
    '03 Euro [CL9]
    Fix of last resort, put a twinloop on it
    2003 CL9 5AT *ECU REFLASHED*
    CT-E Icebox|Ralco RZ pulleys|K&N filter|DC Header|250cell Cat|Cusco Tower & H Brace| H.Drive Coilovers | Rays RE30 18x8.5 | S/S Brakelines | Rigid Collars

  10. #10
    Quote Originally Posted by Fredoops View Post
    Fix of last resort, put a twinloop on it
    It's basically just before the muffler anyway. Probably should have posted this picture before. Showing where the Helmholtz resonator is located.

    Sent from my Pixel XL using Tapatalk

  11. #11
    Member Array
    Join Date
    Oct 2010
    Location
    Melb
    Car:
    '03 Euro [CL9]
    You sure that location being almost at the T junction is not causing extra reverberation?
    2003 CL9 5AT *ECU REFLASHED*
    CT-E Icebox|Ralco RZ pulleys|K&N filter|DC Header|250cell Cat|Cusco Tower & H Brace| H.Drive Coilovers | Rays RE30 18x8.5 | S/S Brakelines | Rigid Collars

  12. #12
    Quote Originally Posted by Fredoops View Post
    You sure that location being almost at the T junction is not causing extra reverberation?
    No idea to be honest.
    But I really don't have anywhere else to place it, as the current location moves into the passenger side of the car utilising one of the hangers from the second muffler.

    It's just ease of placement


    Sent from my Pixel XL using Tapatalk

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