Well, I got the bike fixed and there was a slot available down at my dyno Friday morning, so off I trotted blurry eyed first thing.... nervously, to get this round of testing completed and see where we were at...
So before going any further, let's just recap briefly what the purpose of all this stuff has been.
First, a good few years ago I had a virus that attacked certain parts of my brain and caused permanent damage. As a result I haven't been able to work and my capacity to function has seriously been limited ever since. I've also not been able to ride my bike, hence my appearances on the forum are sporadic at best. However, instead of going completely mad doing nothing, I decided to go along and do something completely mad instead, during the periods where I've been up to doing something. That's why it has taken me as long as it has to get this far!
Anyway, I took a bit of an interest in exhaust system design and first built a race system like pretty much all of the others on the market just to see if I could get something pretty good - I did and it worked.
I then started thinking about the noise issues and thought about whether it would be possible to build a system that not only allowed decent power output, but was quiet, by comparison too. Not too quiet, mind you.
So what do I mean by quiet?
When I was racing in supermoto, we had big exhaust pipes with straight through silencers we're all familiar with that have a perforated tube inside with packing going around them. These pipes are usually considered to give the most amount of power for a single.
The problem with these pipes is that although they were always supposed to be limited to a noise output of 98dbA, in reality we could never even get close to that. I received a drive-by noise measurement from a Yamaha 450 with a motorcross silencer which was in the order of 130dbA.
The other problem is that in order to even get close to the 98dbA limit, the exit of the silencer had to be reduced slightly and they have to be repacked with new packing on a very regular basis. At a motorcross meeting the bikes might pass a noise test on the Friday but by Sunday, the packing would have deteriorated so much a bike would be unlikely to pass the test again. The other thing is that as the packing deteriorates there is also a tendency towards a reduction in engine performance too.
First off I wanted to make something that didn't have any packing in it and therefore it would be maintenance free and a consistent noise output at only 98dbA without excessive power loss.
It then became clear that noise was becoming more and more of a problem for all of us, even at enduro events, so I re-drew my parameters to aim for achieving several levels of noise performance: 1)90dbA, 2)94dbA and 3) a loud system for road race circuits of 98dbA. There was also a 4th half aim just to see how quiet I could go.
I also decided that not only did I want to achieve this according to FIM tech regs at 11m/s piston speed it would also be relevant at 13m/s because noise regs were about to tighten even further as are the limitations we all face when wanting to go out and ride.
Initially my performance benchmark was with the full blown race systems like the Akropovic, FP and Doma exhaust all of which I have extensively tested. However, given that even these at quiet venues require a baffled insert to make them quiet enough, they will naturally lose their power output. I noticed that a lot of race silencers, even at road race events need baffles in them to pass noise testing and those baffles eat power.
So, my benchmark changed to using the stock OEM enduro silencer and system - it made more sense that way. Even the OEM enduro silencer (without the spark arrestor fitted to the exit) is a bit touch and go when it comes to noise testing at 11m/s piston speed and tends to need fresh re-packing. In my tests the enduro silencer I have would not pass the 94dbA test at 13m/s.
Power output with the stock silencer, however, is pretty good. With a supemoto race slick I have consistently measured an output of 56 horsepower at the rear wheel but in using something like an Avon Distanza this reduced to about the 53 hp mark, which is fine.
So basically the aim right now is to achieve more power output and less noise output than the standard OEM enduro silencer - given that this is what most people will be upgrading from. With refinements I anticipate that I will be successfully able to take on the full blown big flow mufflers in due course - I'm nearly there right now, I've just got to find about 1-2 more horsepower at the top end of the rev range.
The systems I've made consist of two types, one is a single tail pipe going into a single silencer, just like the standard system, the other is a twin silencer system that a two-into-one-into-two system. The twin silencer exhaust doesn't require any modifications to the bike other than to remove the metal bracket on the right hand side of the bike at the rear.
All in all, I had 15 different combinations to test and here are the dyno runs for single and twin tests that are for now relevant. The OEM run is in bold in the pictures and the t after the silencer number denotes a twin and s a single:
#1s - very quiet not great power unless you're trail riding
#1t - very quiet and pretty good power
#2s
#2t
#2t and #3t
98dbA silencers - #4s and #5s
As you will notice, two of the twin silencer systems , #2 and #3 produce significantly better power across the entire rev range than oem. Both of these produce significantly less noise, one of them half the sound energy, the other less than half and both of them would easily pass FIM enduro noise tests.
As a result of the tests, for now I have chosen two silencer designs with two single exhaust systems and two twin exhaust systems to take further which I will build so that they can be real world tested on a couple of bikes in extreme conditions, both in supermoto and in enduro environments. One of the systems, the one which doesn't produce much power on the 650 looks like it might be ideal for the 450, however. These are #1s and t and #2 s and t
Overall, each of the options I have chosen to take forwards are below 94dbA at a piston speed of 13m/s, and one is below 90dbA. In actually fact with minor adjustments, one currently looks like it would pass the British Standard test for road legal replacement exhaust systems (82dbA under acceleration load).
I know this is all a bit of an anorac kind of thing, but I hope it is of interest to people other than just me. I'm certainly enjoying the challenge.
All the best,
Simon
PS, eventually, I will look at a US Fire Service approved spark arrester, but that is to come.[/img]
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