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Muffler mods and making

Keeping the noise down at the site

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cymaz10/05/2020 15:18:05
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9253 forum posts
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A bit of a preamble before we start, our site has a noise limit of 84dB @ 7m. As we know a lot ( if not all) petrol 2 strokes are as noisy as hell and the exhaust and sound is just diverted through a cheap nasty aluminium canister.

The old engine from the Wot4 XL passed the test and was under tghe limit. The 30cc that’s just gone in will in no way pass.

It dawn on me today that I’ve a spare exhaust and that I should really start making something up......

The end cut from the canister and housing the baffle ring

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Muffler tubes cut and placed in the baffle ring...

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Tubes inserted, the gasses must go through the front chamber into the tubes to get to the outlet

f8d9f46b-7b04-49b4-bbfb-5e0fe9fcf1b7.jpeg

 

However, someone more clever than me might suggest how to cut the baffle tubes to make it as long as possible for the gas to go before it exits. 

I’ve made a sketch on the pipes showing cut lines for the bandsaw....( the thick black line is where the baffle ring sits) far easier than drilling holes I think. Any thoughts?

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Edited By cymaz on 10/05/2020 15:22:01

Edited By cymaz on 10/05/2020 15:23:22

Engine Doctor13/05/2020 14:08:23
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Hi Cymaz . I recently tried this with a silencer on a pressure washer that my son bought . It was horrifically loud so needed a few mods. I extended the fitted muffler with a tube like you have fitted and used small holes instead of slots . this extended out of the original silencer and I then made welded a absorption type silencer onto the stub . Still loud but stopped the crackle that hurt the ears . Hope you have better luck . I have made some in cowl silencers in the past that have worked reasonably well .

Krumschied silencers are excellent but at £70 to £100 a pop are too expensive to cut open and copy . Have you finished it yet ? Is it any quieter ?

Engine Doctor26/05/2020 12:39:06
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Hi Cymaz. Any luck with the silencer mods yet ?

Nigel R26/05/2020 13:48:25
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Am I right in thinking the first chamber should be the largest of the two?

I seem to remember it can amplify noise if it is the other way around, although I am far from certain on this...

Cuban826/05/2020 13:49:41
2956 forum posts
1 photos

One of my club mates also did a mod similar to the one in your photos - on a DLE 'racket maker' IIRC but also packed the canister with metal pan scourer............not the Brillo variety, but the stuff that is made from shiny strips of metal with no soap. Worked very well, he just needed to experiment with the amount of material to be packed in to get the best effect without too much back pressure.

My old Two stroke motorbikes had something similar wrapped around the exhaust baffles, but made from fibre glass. Was very effective given the increase in noise if you took the stuff out.

Edited By Cuban8 on 26/05/2020 13:52:41

Martin Harris26/05/2020 23:03:08
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9333 forum posts
249 photos

This:

z38 silencer.jpg

...is the inside of the silencer on my Zenoah 38 after I removed the lid to check it. I can't claim any credit for as it was installed on a model which came my way some years ago. It is built in to a die cast project box and seems very effective.

bert baker26/05/2020 23:56:18
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1609 forum posts
331 photos

There was a article in a mag a few years back based on a Zenoah G38,

cymaz27/05/2020 00:18:29
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9253 forum posts
1195 photos

The engine tested for the noise metering is a RCGF30cc, originally marketed by HK. Ive had hours of fruitless tinkering trying to get the thing reliable. I thought I’d sorted it but after it’s second run today it was back to its old self. There is a new carb and gasket set on the way from Aliexpress......again.

Anyway, I’m hacked off with it so got myself a shiny DLE30 from Steve Webb. £239.99 and free 48hr carriage. Best deal I could find. I’ve also purchased a wrap around Pitts style exhaust from A&J Hobbies ( Hobbyprosdepot.com) in Canada). Works out at about £55 including the p&p.

That’s a bit of a tale but there you are.......back to the muffler experiment.....

It did sound less tinnier and more low frequency. Didn’t get it 84dB or under. I was surprised as the change of note was noticeably different. Noise measured at just under the original 90dB. The aluminium solder I bought is weird stuff but after a bit of practice it was successful and all the joints didn’t leak and stayed together. The product was DURAFIX from Oxford Welding Supplies. The instructions are quite specific but I managed to get a reasonable finish in the end.

I bought a pepper pot for a standard DLE 30cc exhaust. This was measured and was on 84dB @ 7m. A pass in the confined garden. However the engine lost 680rpm @ WOT.

Work in progress methinks.

cymaz27/05/2020 00:24:09
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9253 forum posts
1195 photos

BTW, I’ve got some stainless steel pan scourers in the draw just to be on the safe side, should the fancy take me

bert baker27/05/2020 01:20:20
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1609 forum posts
331 photos

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bert baker27/05/2020 01:22:47
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1609 forum posts
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I did make a multiple chamber Pitts style exhaust for a DLE30

I did use a original and just extended it with thick wall aluminium

the things we do for fun

Rich too27/05/2020 05:38:14
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3060 forum posts
1070 photos

Header and cannister is a lot more effective but obviously take up a lot more room. HK used to sell them pretty cheap too.

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