Decibels

[fatboyracing]

Hi Guys,
When I started with my 73 XL 350 it had a reading of 114db
I removed the muffler and pulled it apart drilled all the holes in the perferated tube bigger and added more
I repacked the muffler
reading 104db down 10db for not much work
I then rapped the hole header pipe with the heatproof cloth tape (a bit like drag cars do)
reading 99.8db gained another 4.2db for $50 bucks
now I only have to find 0.9 db to be legal I think i will start with the engine noise next

I think that if we try , it can be acheaved ,Im not saying it is easy

cheers
Fatboy

ps Greame get the spell checker back please im a shithouse speller.

[pokey]

Back in about 1980 i was fortunate to have a reasonably fast 750 water bottle with chambers but seems the local rego guy didnt like the music it made, neither did my mum.

It was either put the stock exhaust back on or quiet he beasty. solution ... expanded steel wire mesh 



I removed the baffles and rolled the mesh into a tube and fabricated end plates and rivetted it all together and repacked with glass wool.

Result... quieter than the stock pipes.

It was a cheap fix and worked beautifully with no noticable change in power, just make sure you  have the mesh facing the right way or it dont do squat.

Was still reasonably quiet unpacked.

[firko]

I built the muffler on my square barrell Maico using the rolled expanded metal method as Pokey described. Although the decibel reading of the bike hasn't been tested to my knowledge, I know that the bike was decidedly quieter than other Maicos at the Coffs Nats. Tony T even commented to me on its different sound. I'm curious to have the decibel reading checked at CD5.

Rather than treating this 96db limit as the shitty break that it indeed is, we must now look at the challenge of getting our bikes in under the limit. I reckon that because us vintage folks are largely do-it-yourself oriented, we should overcome the noise obstacle using some innovative methods and be seen to be showing the way for the future.
Below, is my Maico showing the homemade muffler that I reckon will come close to passing 96db.

[evo550]

How many of you have been tested in the past? Remember noise limits have been around along time, 102db last year, I bet very few bikes would have met that limit if tested. So why all the yelling and screaming now?
I have been racing for decades like most of you, and have only ever once seen a noise test carried out, and that was at the end of last year at my local "Modern" club where they where pro activly testing bikes to see how many bikes would pass the new level...if ever tested.
 Ma are not KILLING the sport with this move they are trying to prolong it for us and our kids, get a muffler and stick it on the end of your pipe....make the forkin' thing 96 db and stop whinging.

[yzhilly]

What size holes are we talking about in the expanded mesh , I'm gonna try that on my YZ100 .

[pokey]

unsure what size i used hilly as it was a while ago and i used a bit of scrap.  Maybe 0.8 thickness.Pop down to Bunnings they should have a  a nice small sheet to play with.

 Firko may know metal sizes being a boily.

 just ensure the  openings face the engine when you install.

[firko]

Me too Hilly. I built my muffler in 1995 or therabouts but honestly can't remember the size of the mesh. Use steel and not Aluminium as the alloy heats up and distorts. Something with a 7-10mm slot should do it.

[Doc]

YZhilly..the holes are only about 2x3mm max and the mesh is formed from a single sheet of steel or aluminium by pressing. The fluted holes can be used either way..the gasses can flow over or they can flow against kinda like a cheese grater affect. Expamet used to be the main supplier of this stuff in anything up to walkway mesh size. It's good shit but it's expensive. The aluminium stuff is the go, light as a feather and it forms and cuts easily. It does work as I used this in all my mufflers years ago when I had a ready supply. The aluminium stuff is used extensively in satelite dishes and the product name is 602DV or 602DVA for the aluminium. If you can get it at bunnings I'll be buying some myself for sure!

Incidently, the quiet muffler on my TM has the muffler built using the bent but now perforated stinger pipe as the inner. This seems to keep the noise down and it doesn't seem to rob power as it keeps the stinger at the desired length. The outer is simply a piece of 2 inch exhaust with a kink to match the stinger...hmmmm..pic needed..will get one when it's light 

[GMC]

I agree with 414 - where are you Geoff???  My 250 Elsinore has a GMC pipe with something like an 18inch silencer packed to the max and should be OK - my YZ360 on the other hand has a bloody 3 inch pickle!!!!!  Geoff - what ya got for my 360 mate!

 

Rossco

When I started to get serious about making chambers in the early nineties I purposely made an effort to build them with good mufflers as I believe that loud bikes do us all a disservice.  I generally made the muffler lengths 300mm long, which was longer than anything else around that I saw or they ever came with. Some of these pipes, Maico & CZ 400's for example have given me good feedback with performance despite these long mufflers.
A lot of my downpipes are similar in this way with the muffler tube around 400 long but 100 of that is the last baffle cone leaving 300 for the muffler core.
I just don't have the time or recourse for testing at the moment, flat out getting stuff ready for CD5 where I am hoping to get some feedback from some of my pipes that may be there. If these 300 long mufflers are enough to make the new limit then it won't be that hard to achieve but if not then I'm not sure what else as I can't make these mufflers any longer as they would ported past the back wheel which is another no-no.
Future muffler decisions will be made after CD5

I will also have my muffler packing on special at CD5 as I did with the other CD's

The expamet mesh is available either flattened or with the flutes protruding, I would be careful with some of this as the flutes can prematurely allow the packing blow out. Too large a hole in the perf mesh can do this too, which brings me to another point. Do the bikes have to meet the test before a race & after a race or just at scutineering???

Ceramic coating of pipes may help with the resonating sound from thin wall pipes too, not sure just a thought.

[Rosco400]

Do the bikes have to meet the test before a race & after a race or just at scutineering???

At the NATS last year at Coffs, they were testing as you come off the track so guess that would be standard practice

[mboddy]

If these 300 long mufflers are enough to make the new limit then it won't be that hard to achieve but if not then I'm not sure what else as I can't make these mufflers any longer as they would ported past the back wheel which is another no-no.

The stinger before the muffler can be extended back into the body.
This has been used successfully in the past on bikes like the TZ750.
My TDR comes from the factory like this.
It does not reduce the power output but it does reduce the noise a lot.

For more detail see '10.16 Tailpipes' in 'The High-Performance Two-Stroke Engine' by Dr John C. Dixon. Haynes 2005.

[Doc]

This is what I was talking about..doesn't look the prettiest but it is far quieter and it works better than any 'after stinger' type muffling I've tried. I'd guestimate about 30% quieter than a TM pipe with the standard pickle type muffler which I run on the other TM

[mboddy]

Just been trying to quieten the IT250D down.
Down to 3 disks in the Supertrapp.
A pvc end cap filled with stainless steel scourers.
Smaller diameter core.
The nasty crackle is gone which would have blown the noise meter.
But I have no idea whether it is quiet enough or not.
I hope it is quiet enough for Heaven Round 2 next weekend.

[fatboyracing]

Hi Guys,
Just got back from Testing modern bikes in Penguin at the first round of the Australian Motocross Champs
tested  75 on Saturday and all passed easy
remember that the reading only needs to be 98.9 with a type 2 meter
most of the factory bikes came in around 93 to 95 not much over. They are also careful not to be too close before the race because after a 30 min moto the pipe gains about three quarter to a full db in noise,and in the races 1st, 2nd and 3rd were tested after racing.
Most of the factory bikes were tested sometimes 5 times playing around with end caps etc. perhaps thats were we should be looking.

I also will be helping Derek Rumble test at CD5

Cheers
Fatboy

[mboddy]

Gina convinced me to get a noise meter.
I then spent the afternoon trying to get the noise down.
It isn't too bad now at a fast idle.
Didn't have a rev counter and so I still don't know what it puts out at the prescribed revs.
I would like to get it much quieter.