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Exhaust Noise

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#1 weazel134


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Posted 11 September 2018 - 02:27 PM

Was at a track day yesterday and was told I was very close to the noise limit and had to short shift to keep the noise level down. I have the standard GBS exhaust silencer. The question is, if I were to add more wadding would this help with noise level? Would it hinder the performance?


#2 theduck



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Posted 11 September 2018 - 02:46 PM

People have mixed results with adding more wadding, as its possible to have too much for the size of the silencer.  Peronally Id just buy a bigger / more efficient silencer for use on track days.  

#3 brumster


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Posted 11 September 2018 - 06:29 PM

I would inspect it first and just check how much wadding is still in it - it might have blown/burnt it all out, in which case yes you'll see an improvement :)

#4 kevin the chicken

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Posted 11 September 2018 - 06:39 PM

I put a bigger exhaust on and it didn't seem to make much difference to the noise. Bought some earplugs that sorted it. Wouldn't help with track limits though.

#5 agent_zed


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Posted 11 September 2018 - 06:41 PM

I am certainly far from an authority on this so this is just my thinking along the lines of the above. You don't want too much and you don't want too little. 


If the gbs silencer is a straight through you'll have a perforated pipe to allow the soundwaves to be absorbed by the glassfibre wadding. my thinking is if you pack it too tightly you will create a wall against which the sound can't penetrate and it will be reflected back. Too little and and the sound will travel through the wadding and be reflected back off the inside of the can.


The problem i am finding is that glassfibre eventually gets broken down and blown out. It's always going to be a problem as by leaving a gap (less hard packed wadding) for the sound you are allowing more gasses to penetrate. I guess you have to just assume repacking is part of the service schedule.


I've heard some people use stainless pot scourers as they don't break down the same. I'm going to try this soon (on the long list of jobs).

#6 knights_templar


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Posted 11 September 2018 - 06:44 PM

standard early type or standard late type with large cylinder?


If later type does it have the built in CAT?

#7 James24785


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Posted 11 September 2018 - 06:55 PM

Mine has the standard early type and I had no problems at donnington a few weeks back

#8 cb750


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Posted 11 September 2018 - 06:58 PM

I used Acousta-Fil when I repacked my silencer. This is in flexible compressed sheet form that expands when heat hits it to fill the silencer with the correct density. The supplier gave the correct amount for the size of silencer. Problem is I can't find where I bought it from!

#9 weazel134


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Posted 11 September 2018 - 07:05 PM

Thanks for the advise guys. I was at Bedford autodrome which has unusually high standards with regards to noise. My exhaust silencer is the GBS new type without cat. When I was at rockingham it wasnt a problem. Just think a couple of db S lower would cure the problem.

#10 Longboarder


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Posted 12 September 2018 - 09:39 AM

Putting in a small expansion box had a huge effect on mine many years ago. The one shown was an old silencer, gutted and shortened to about 10" long to fit. Have since fitted a 21" x 6" which is OK but not as quiet as the expansion box + small silencer and looks huge and ugly.

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Edited by Longboarder, 12 September 2018 - 09:40 AM.

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#11 richyb66


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Posted 12 September 2018 - 10:44 AM

Have a look at the Supertrapp clamp on silencer. You can add or remove diffuser discs to tune the noise level. Obviously increasing the back pressure to reduce noise will have an effect on power, but there's no point in getting maximum power if they won't let you on the track.

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