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Decat noise

Discussion in 'Land Rover Discovery' started by Captain Magic, Jun 20, 2017.

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  1. Captain Magic

    Captain Magic Member

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    Morning peeps, I know that the td5 decat subject has been done to death over the years, but what I'm struggling to find by looking back is any information about increase in noise or change of exhaust note. I put a decat pipe on mine yesterday, and now there is a noticeable change in exhaust note, it's a deep sound which occurs when under load, and between 1250 and 2000rpm. Has anyone else noticed this?
     
  2. RyanDay1

    RyanDay1 Well-Known Member

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    I absolutely love mine, will soon be deleting silencer too, its a deep roar which hits the most under load at 1600 revs for me, with a little turbo whistle as well, mines been remapped too not sure how much that afffects sound but I think the decat makes it sound like it should, but not overly loud with the silencer still in place :)
     
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  3. Captain Magic

    Captain Magic Member

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    So it's not just mine then. The reason I ask is because I had a rattle in the exhaust. It turned out to be a loose baffle in the centre silencer, but I thought that it could be the flexi joint, so seen as I was going to decat it anyway, I started with the front pipe. This made the silencer rattle even louder, so I put a klarius silencer on from eurocar parts (not wanting to go with a cheap britpart one). This is when I picked up on the noise\ roar. I wondered if my new silencer was dodgy. Do you know of anyone who does a decat pipe with a silencer to get rid of the roar? Also, do all pre 2002 discovery's have this exhaust noise, because they never had cats fitted, and from what I can tell, the two silencers are the same part numbers as my 2004 model?
     
  4. RyanDay1

    RyanDay1 Well-Known Member

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    Mine also has a very slight rattle on occasion which I suspect is from the joints of the centre pipe, I'm not sure about whether there are decat pipes with silencers as they're based on performance so to remove the restriction but if you really dont like the sweet rumble then a decat pipe could be fabricated with a small silencer to replace the cat I guess, maybe an old back box silencer could be used, but that would make 3 silencers, which asks about the discos which dont have cats in the first place as you say
     
  5. Captain Magic

    Captain Magic Member

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    When did they alter the bhp from 136 to 139? I wonder if this has anything to do with the pre cat ones being quieter?
     
  6. Captain Magic

    Captain Magic Member

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    Right guys, it's been a while since I started this thread, and after some on and off research and enquiries I think I've got somewhere. It turns out that the booming noise was exhaust resonance, caused by the frequency of gasses in the pipe. By fitting the aftermarket decat pipe, which is lighter than the pipe with the cat in, you decrease the density of that part of the exhaust, leading to vibrations at certain revs, 1500 to 2000 in my case. It was suggested to me that adding weight to the new pipe would increase the density of it overall, and might decrease the resonance. I was sceptical at first, but I gave it a go, and it WORKED. The more weight I added, the less resonance there was, and it appeared lower down the rev range. I now only have a slight rumble at about 1200 rpm under load, and that is only because I ran out of iron bar.

    I hope this helps someone somewhere
     

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