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March 29th, 2007, 05:49 AM   #1
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Exhaust system and silencer in the making (update)

Hello All,

Some of you may remember that some time ago I embarked on a little project to design and build my own exhaust system. I've had some other things on my plate preventing me from spending much time on this which is why it has taken so long and progress is so slow. However, when I started it was just to build a normal race system that could hold up against the ones available on the market.

The results were pretty good. Having tested all the one available on the market and compared them back to back, my personal choice was to make something that was equal to the Doma system in terms of characteristics.

The result, as in the dyno chart below. My system is red, the Doma in Blue. I was happy with this.

My system v Doma

While making this system I'd had to learn quite a lot about exhaust systems and their theory and one point that had really started to get to me was about silencers. Now, whatever you might think of them, the current designs using any type of absorption material tend to be pretty crap. Mainly because they actually need maintenance (a lot of it when you're having lots of stringent noise tests) and they're actually not particularly good at the job they're supposed to do.

So, I got a bee in my bonnet about going out and looking at the options and began a project on designing something that might work a little better. A little after I began, noise restriction really started to play a major role at circuits right around our country with many people having to lose power by inserting quiet cores or using highly restrictive silencers to get away with it.

My project was defined - a high power output yet efficient silencer that was quiet but gave out a “goodâ€
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March 29th, 2007, 08:01 AM   #2
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Hi there Simon,

very, very impressive! What an awesome job you did and still doing
I like your 'sufficient power/less noise philosophy'...

I did SPL measuring during carry on a business for High End HiFi speakers
some years ago. So I have a good idea about your extraordinary charges.

I considered to design my own exhaust too but while examine the problems
more closely I surrendered... Much to complex...

Nevertheless I designed and built a small and quite silencer for my 125ccm pit bike.

I'm very interested in your twin project. Always wanted something like this for
my FS 650. Really looking froward to the results of your power runs!

Do you thing there'll be a chance we can purchase your cans one day?
Would be great!

Again kudos to you!

Regards,
Maddel
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March 29th, 2007, 11:23 AM   #3
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Originally Posted by Maddel

Do you thing there'll be a chance we can purchase your cans one day?
Would be great!

Again kudos to you!

Regards,
Maddel
Hey Maddel,

Thank you for your support - and understanding

I would sincerely hope that at some point I could get some manufactured and I have spoken to a kindly manufacturer about the possibilities. However, I wouldn't want to get hopes up too much just in case the other things going get in the way. All I can say is watch this space.

If they don't come to anything in terms of me making them available, then I have considered sharing the specs at some point in the future so other individuals could make them up or have them made for personal use. We'll see.

Cheers,
Simon
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March 30th, 2007, 12:03 AM   #4
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Outstanding work Simon and so on...

Sign me up for a 'not less power than a Doma but hell'uva lot quieter'-system right now

This is truly what our belowed sport needs, at least here in Sweden with almost silly noise restrictions at local tracks.

Keep up the good work !!!
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March 30th, 2007, 06:11 AM   #5
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Simon.

When I saw you at your short stay visiting Iceland last summer,you did´nt look strange at all.
Hell, I even sat in a chair beside you for quite some time before I figured out that you were the famous "SilencerSimon" and you figerd that I was Me.

But you are utterly insane, Simon.
Consider this as a comliment. Without insane people running loose, the world would be poorer.

Finish your work "SilencerSimon" .
Your results are fantastic as is. Shows us lesser mortals what kind of crummy crap some are spending for Doma, Akrapovitcj,whatever kind of loud junk !!

My deepest condolences to your wife, by the way........

Heimir Bardason.
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March 31st, 2007, 07:14 AM   #6
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High Performance Exhaust

My compliments to you for your endeavor. I wonder if Akropovic studies such things in this detail.

My question is, can you explain how you can achieve silencing without packing? Also, would it improve power by using a tapered outlet pipe, i.e. megaphone style? The White Brothers e-series used this and it seemed to improve gas flow vs. a straight pipe, especially at higher rpm.
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March 31st, 2007, 11:48 AM   #7
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Originally Posted by HeimirBardason
Simon.

When I saw you at your short stay visiting Iceland last summer,you did´nt look strange at all.
Hell, I even sat in a chair beside you for quite some time before I figured out that you were the famous "SilencerSimon" and you figerd that I was Me.

But you are utterly insane, Simon.
Consider this as a comliment. Without insane people running loose, the world would be poorer.

Finish your work "SilencerSimon" .
Your results are fantastic as is. Shows us lesser mortals what kind of crummy crap some are spending for Doma, Akrapovitcj,whatever kind of loud junk !!

My deepest condolences to your wife, by the way........

Heimir Bardason.
Hello there Mr. Bardason!

So glad to hear from you. I was thinking of you only recently - we were climbing another volcano funnily enough!

I have passed on your condolences to my wife and they are truly appreciated. It is a rare thing that she receives genuine understanding and sympathy (that's what she tells me, anyway, as if I possessed none).

I really don't know where you're coming from on that insanity angle though, and I know even less where the nickname of mad professor has come from either

I do thank you for your support however, as always, but just to really put the fear into you, our wonderful experience of "fire and ice" not only made me determined to come and experience a lot more but it also really fuelled my interest in the next project I'm planning to embark upon - but you'll be happy to know that it won't belong here on the Husaberg forum

We hope you and your family are all keeping well and, as I am sure you know, our door is always open to you should you be in our neck of the woods. We genuinely hope we can return your hospitality someday.

Simon
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March 31st, 2007, 12:29 PM   #8
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Originally Posted by Jocke_D
Outstanding work Simon and so on...

Sign me up for a 'not less power than a Doma but hell'uva lot quieter'-system right now

This is truly what our belowed sport needs, at least here in Sweden with almost silly noise restrictions at local tracks.

Keep up the good work !!!
Thank you Jocke, we're also experiencing troubles at the circuit but I can only imagine what Sweden might be like

Simon
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March 31st, 2007, 01:01 PM   #9
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Re: High Performance Exhaust

Originally Posted by Motodude
My compliments to you for your endeavor. I wonder if Akropovic studies such things in this detail.

My question is, can you explain how you can achieve silencing without packing? Also, would it improve power by using a tapered outlet pipe, i.e. megaphone style? The White Brothers e-series used this and it seemed to improve gas flow vs. a straight pipe, especially at higher rpm.
Thank you Motodude. I'd certainly hope that Akro do study these things in such detail and I'm sure that if they wanted to they could do some very good stuff in this area.

With regard to achieving silencing without packing, I'll try to give a simple explanation. I obviously don't know how technical you are so please excuse me if any of it is too basic for you, I don't mean to patronise or anything like that.

The "normal" silencer use on our bikes using packing as the silencing solution is usually termed as an absorptive silencer. The ones I am working on are essentially reactive.

It helps if we look back to the history of silencers to gain a better understanding.

During the industrial revolution they found that one of the most effective ways to muffle exhaust noise from machinery was to let all the exhaust gas into a massive room and sometimes this room was buried in the ground. Essentially the exhaust gases would expand into these massive chambers and bounce around alot and the noise would dissipate through a transfer of sound energy into heat energy. On a motorcycle using an absorptive silencer the principle is largely the same. The exhaust gasses enter into the silencer and the sound waves as well as some of the gas expand into the packed chamber. Now, the absorptive part is that the packing that is put into these silencers adds viscosity to the chamber so that certain frequencies of sound require more energy to travel through the packing and instead dissipate into heat energy in the packing.

Many people incorrectly assume that a normal absoptive silencer because it is "straight through" it doesn't produce back pressure but in actually fact they do build back pressure and some of them quite a lot.

The silencers I am working on utilise the sound energy of the exhaust to combat the sound of the exhaust as well as other techniques that use an understanding of the behaviour of sound to minimise it.

A really simple example of this is a resonator that most people know as a Helmholtz resonator. The simplest example of this is a beer bottle when you blow air across it you get a sound which frequency depends on the size of the empty chamber in the bottle. This effect, for example can be used to quieten and exhaust in that you can design a chamber that resonates at a frequency that is opposite to one that is troubling you from the engine. The noise cancels itself out (in reality it never completely cancels itself out but you get the meaning).

Helmholtz resonators are useful however they are only effectvie for very narrow frequency ranges, not for the broad range required for an engine - unless there is a particular frequency causing a problem.

So, the reactive silencer is designed to work with and against the noise the engine produces by using the sound energy already there as well trapping and dissipating it through heat energy while not trapping the exhaust gasses - therefore no packing required.

I hope this helps.
Simon
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April 1st, 2007, 03:10 AM   #10
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Sorry Motodude, I forgot to answer your question re using tapered pipes.

The simple answer is: yes the cone or taper can be used to improve power output.

When you have the sounds waves travelling through the exhaust pipe, when they get to a step in pipe diameter, or even the end of the pipe, sound waves are transmitted back up the pipe towards the cylinder. This effect is called rarefraction. This phenomenom can be used in straight pipes so that at certain engine rpm the exhaust pipe is designed so that the sound waves travel back in such a manner that there is low pressure in the area just past the exhaust valves so the exhaust gas has an easier time expanding out.

With a pipe taper you are essentially building in lots of smaller sound waves going back to the cylinder so you can in theory build in this low pressure effect over a longer range of engine rpm. In addition, it has been found that a cone with a reverse cone afterwards works very well too - look at 2-stroke exhaust systems.

In some systems on the market, I have found that the various tapers they add to the system don't actually give any practical benefits over a well designed straight pipe, thus they're over engineered and unnecessary. In some systems with tapers they work absolutely brilliantly.

At present, my foray into the exhaust system has only utilised one minor taper at a critical juncture, but I have stuck to investigating the possibilities of getting the power and drivability from simple (thus cheaper) straight pipes only. I haven't needed the taper yet, so to speak, but they may come along in time

Simon
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