32 replies to this topic

[MartinS]

I know a few people have been having trouble with track noise limits and things will only get worse, and wondered why no one designs simple decibel reduction systems for our cars, especially as there are some serious engineers on this site. As my exhaust has got notaby louder since supercharging the car (the exhaust was designed for it when it had 185 bhp), and as I am doing goodwood in 3 weeks, thought I would try something. I bought two db reducers from demon tweeks (£15), cut them down so they would go in, drilled holes in them and fitted them via bolts that push outwards (theres an inner lip on my exhaust that holds them in). I then took it to Goodwood to get a db check done. Amazingly I recorded 96db with the tubes in, 99db with them out (wasnt as bad as I thought). Its not a huge difference but may be enough in some situations and I will just keep them in my tool bag now in case. Martin s

[dw1]

TTIWWP Great post, sounds like that could be a winner, pics please

[smiley]

Browsing through the tweeks website, but cannot find them. Do you have a direct link?

[Gizmotron]

I know a few people have been having trouble with track noise limits and things will only get worse, and wondered why no one designs simple decibel reduction systems for our cars, especially as there are some serious engineers on this site.
As my exhaust has got notaby louder since supercharging the car (the exhaust was designed for it when it had 185 bhp), and as I am doing goodwood in 3 weeks, thought I would try something.

I bought two db reducers from demon tweeks (£15), cut them down so they would go in, drilled holes in them and fitted them via bolts that push outwards (theres an inner lip on my exhaust that holds them in).

I then took it to Goodwood to get a db check done. Amazingly I recorded 96db with the tubes in, 99db with them out (wasnt as bad as I thought). Its not a huge difference but may be enough in some situations and I will just keep them in my tool bag now in case.

Martin s

What exhaust system do you have? i have a Larini backbox and the rest is miltek. i am also worried about the db's readings especially at tracks that test whilst driving pass check spots like Bedford. if these db reducers work it would save me change the exhaust for some track days

[The Batman]

you wont get anywhere near bedford with a larini he has a 2ublar and can you post some picures and links please martin

[MartinS]

Page 301, 2 inch inserts in the demon tweeks catalogue. You have to cut them right down as our exhuast bends quite quickly. I had read that to reduce noise you need to break up the flow, so cut fine strips in at the ends and folded them in in a star like pattern, and then drilled additional holes in the tube. I did this once before and had to drill holes in the exhaust it self to hold them in, but this time I had a different exhaust and didnt have to do that. I'm sure there must be some other cleverer ways of holding it in. My system is a 4-1 TMS manifold, Miltek cat, and 2tubular 2.75 inch silencer. I have tried to attach pictures with no luck. As I said, I'm sure someone on here could make something way better. Martin ps BRG Pete also has some db reduction tubes in, that you can get off ebay for £10 each. They were to thin for my exhaust but might be better for others, and they already had lost of baffling (holes, etc) work done on them.

Edited by MartinS, 22 February 2010 - 01:04 PM.

[BRG_Pete]

Good to hear that you found some that fitted + worked

[smiley]

Martin, Can you lookup the brand name of the silenser in your catalogue, so i can try to find it's online equivalent?

[peterg]

Demon Tweeks online catalogue here http://publications....12581/00048044/ open the front cover and scroll down the index on page 3 and click on 'Exhausts' page 298 then turn the page over to display 300 and 301 and it's at the top left of page 301 actually that then refers back to page 298 where the measurements and prices are PS: they're called "Decibel Inserts"

Edited by peterg, 22 February 2010 - 01:31 PM.

[The Batman]

here:



did you have to drill the tailpipes to bolt them in then martin?

[JimmyJamJerusalem]

did you have to drill the tailpipes to bolt them in then martin?

No the whole thing goes inside, and the bolts jack themselves against the inner surface of the pipe. At least THAT IS WHAT MARTIN SAID IN THE OPENING POST

[The Batman]

lol just making sure, im allowed to make mistakes at this time in the day i only just woke up

[smiley]

Online: http://www.demon-twe...code=JETU935130 Then select 2.5" Just ordered a pair. Would be nice to shave a few db off at some pesky tracks.

Edited by smiley, 22 February 2010 - 02:17 PM.

[MartinS]

Mine were the 2 inch, the simple one at the top of page 301 demon tweeks. I think theyre made by jetex, so might be cheaper elsewhere. As my exhaust has a lip on the inside, I was able to use bolts pushing outwards and up against that lip to hold it in place (length wise its jammed in at the back). If the exhaust hasnt got a lip on the inside you would possibly have to drill holes or find another way of fitting it. Maybe a good look on a fixings web site may show a better solution. Bikes have some very neat set ups, so I do believe someone on here could make something very good and neater than mine. I dont believe there is any noticable power restriction, but with 250, I could lose a couple and not notice anyway I guess. Martin

[smiley]

Bugger. Thought they were 15 a pop, hence the 2.5 Ah well, i'll put the 2.5's on ebay. Just purchased the 2". I have a janspeed with a lip, so it should work out.

[MartinS]

I'm sure if you explain demon tweeks will refund, theyre pretty good with things like that. martin

[smiley]

return charges are not refundable, so ebay is better. Can you take some ficture of the holes, and cut off you made?

[MartinS]

I'm not sure what you meant in the last post? Martin s

[smiley]

"cut them down so they would go in, drilled holes in them and fitted them via bolts that push outwards " How much did you cut off? (if you could measure up what's left of it?) How do you keep the bolts in place? (so they do not fall out?)

[MartinS]

The amount you cut off, depends on the exhaust you have. Shove in as far as the pipe will go, and mark whats left sticking out, then cut off the appropriate amount so that it goes in as far as it can. As it touches the left wall of the pipe fisrt, it shouldnt reduce flow particularly. How much you want stcking ourside of the original tail pipe is up to you, I left mine longer so it sticks out further as I wanted as much effect as possible. The two pipes wont be the same length.Usually the lower exhaust outlet is slightly shorter. I then cut fine lines in at the inner end of the db reducer and bent in small strips in a crude attempt to break up the airflow. I only drilled holes after my Goodwood sound check, so may not be necessary at all. To hold them in, I put the now cut pipes in to the exhaust, and marked where I would drill holes, just inside my exhausts inner rolled over lip. I drilled the holes and use d bolts to push ouwards inside the exhaust and tight upto the lip. I used double bolts to make sure it was all very secure. The method of securing may vary with each exhaust type, equally there may well be better methods than I used. Martin s