Wednesday, 16 August 2017

Building a DB-Killer that actually works

Most of those universal muffler-tip inserts you can buy out there are all nice and good, if you're *JUST* over the legal noise limit. Now my exhaust on the TR1 and on the XS-Triple-Sidecar weren't a bit over the legal noise level, they had to be silenced quite a bit - which meant around 20db on the TR1 and I didn't check on the XS Triple Sidecar, but it was around the same amount.

That being said, the main flaw of most muffler inserts is, that they don't force the exhaust gas around corners and thereby don't reduce the speed of the escaping gas sufficiently. I sought to change that with this relatively simple design.

I used some big washers turned down so I could weld them to the inside of a tube that would go into the slip-joint of the muffler. 

Cut two lengths of tubes that would fit inside the center hole of said washer and made a plug on the lathe, which would go between said tubes.

And this was my first prototype. The holes were ground with an angle grinder and relatively large compared to the actually used inserts. But it proved a quite dramatic noise reduction was possible.

Without an insert the TR1 was idleing at around 82 to 84db and the amount achieved, with no further damping material (i.e. stainless steel wool pot cleaners) was below 70db. The measurements were taken 1m behind and 1m to the side of the exhaust.

So how does it work: The exhaust gases come in through the center hole, escape through the first hole, have to go all the way round to the other side and escape through the bottom hole. All of which results in a massive reduction of gas-velocity and thus less noise.

In order to make the legal side of things easier on me, I decided to weld them in completely to make sure that during the inspection the engineer wouldn't add a line saying something like "removable muffler-insert" to my papers. As that's what the police always checks first overhere.

Another setup I tried before and which (to my surprise) worked better than expected, were these really simple inserts, basically just comprising of a large washer with a 20mm hole. If you're a bit gentle on the throttle the noise levels up to around 3000 - 3500 rpm are nearly the same (you'd have to have both bikes sitting next to each other to really make out a difference), but especially at higher rpms it's lacking dramatically.

All of that being said, the first set of GreasyGreg Exhausts has been entered into the legal paperwork of my bike and it will certainly not be the last.

Oh and if you're worried, don't the actual registration code of my exhausts is quite a bit longer than that... This is only the "model identifier". Pretty posh, eh? 😎

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