How to reduce the exhaust noise

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
pergarbos
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How to reduce the exhaust noise

Post by pergarbos »

My AJS 18 CS from 57 is making a lot of exhaust noise (as it should) - but if possible -i would like to reduce it. I have seen some headers for 18S where the end of the header is blocked and instead there is a lot of holes around the area / diameter stiching in to the muffler. Does this this have a significant effect on the noise as well as the performance or is it an acceptable solution. If so i could easy modify my competition header to same design since around 120 mm af the header already is sticking into the muffler.

Anyone having experience with this type of header

BR Per
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Rob Harknett
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Re: How to reduce the exhaust noise

Post by Rob Harknett »

I believe original pipes that had the end blocked, were such, as this was the baffle. Repro's have a shorter straight through pipe with baffle in the silencer. Having both will not allow gases to escape properly, back pressure will effect performance. If you have a clean engine and new exhaust, the bike may sound noisy. It will quieten quite a bit when the system get's a bit of carbon build up. Which again should be kept clean to avoid back pressure. Although you do not get so much carbon build up with todays cleaner fuels, compared to back in the 50's era. An engine decoke and cleaning exhaust with caustic soda hardly ever needed. Due to cleaner fuel and lower mileage.
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clanger9
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Re: How to reduce the exhaust noise

Post by clanger9 »

A "pepper pot" header will be quieter than a straight-cut header. The perforations allow the the pressure pulse into the silencer more gradually, which takes some of the loud crackle off.
As long as the end of the header is open at the end, it shouldn't affect performance.
1989 Moto Morini Dart 350
1993 Ducati 750SS
pergarbos
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Location: Denmark

Re: How to reduce the exhaust noise

Post by pergarbos »

Thanks a lot for the feedback
Since my muffler is very open (not much restriction - if any) i think i will try with the "pepper pot" modification
as mentioned - it migth not even be needed to block the end of the pipe
cbranni
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Re: How to reduce the exhaust noise

Post by cbranni »

Pepper pot pipe 56 G80cs photo if it of any use.

Image
only dead fish go with the flow
pergarbos
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Re: How to reduce the exhaust noise

Post by pergarbos »

Absoluty - its give me a clear picture what to do. - only one quistion - the header open at the end - rigth ?
cbranni
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Re: How to reduce the exhaust noise

Post by cbranni »

If the header is the exhaust pipe, then the end is closed off and the gasses can only get into the silencer through the series of sixteen 8mm holes.

The new exhaust system I put on my G80cs from Feked is very loud, the exhaust pipe doesn't have the pepper pot set up but I may alter it in the winter.

Colin
only dead fish go with the flow
pergarbos
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Joined: Thu Jul 12, 2018 8:26 pm
Location: Denmark

Re: How to reduce the exhaust noise

Post by pergarbos »

Okay - i see - since my muffler is open i will block the end of the pipe and drill 16 Ø8mm holes similar to the picture.

Thanks again for information / BR Per
Mick D
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Re: How to reduce the exhaust noise

Post by Mick D »

Hi

The area of 16 x 8mm holes equates to a pipe diameter of around 1 - 1/4" - seems a little restrictive.

I know the parts list illustrations are not 'gospel' but they show more holes - they also seem to indicate the pipe is not closed.

Perhaps it may be good to drill some holes and see how they affect the noise output rather than plugging the pipe straight away.

Regards Mick
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ajscomboman
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Re: How to reduce the exhaust noise

Post by ajscomboman »

Interesting subject, I'm just about to go the opposite way. The original pipe for a 56 CS is 42" long straight through with no restriction. My current setup is the same 42" pipe with a silencer on. This seriously restricts the breathing even after I've removed the end baffle. The pipe extends into the silencer 4-5" and restricts the breathing where it nearly contacts the inner baffles to the extent where the bike will not pull full power from 3/4 throttle upwards. The carb setting is fine so I'm sticking with the silencer but cutting the pipe so it just pokes into the silencer enough to clamp securely, and I love the noise!
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