How to get rid of sound dampening inside expansion chamber ?

[jordanrbaker]

I remember when I was 16 I got a Derbi Senda as my first bike, I was always tinkering with it but one day I got bored and cut the expansion chamber in half to find there was sound dampening packing all the way round the wall of the chamber. so I took it all out and welded it back up and wow to sound difference it sounded more like a dirt bike with the tingy sound.


basically I have another on as a project bike now but don't have a welder anymore so is there any other way of removing the dampening inside the expansion chamber ? would using a blow touch and a air compressor work basically burning it out ?


and would a completely emptied stock exhaust be as good as an aftermarket one I know the power band would be different but would hp?

[stinkwheel]

I've deleted the other two iterations of this topic. Please don't post any more. One post on each subject is sufficient and yes, the workshop section is the place for this one.

The packing is fibreglass, it's not flammable.

I doubt there was any packing inside the expansion chamber. I think you may be confusing the silencer with the expansion chamber. The expansion chamber is the really wide bulgy bit that curves round the front of the engine.

In general, messing about with the silencer on its own will make a bike SOUND faster/louder but GO slower or potentially, especially with a 2-stroke, experience a catastrophic engine failure due to having the wrong fuel air mix.
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[jordanrbaker]

[jordanrbaker]

[Teflon-Mike]

The principl;e of the two-stroke expenaion chamber is Kaaden effects.

Clever German chap in the 1950's, and engineer at MZ; he wasn't allowed under Russian Planned ecconomics to build an engine to go racing; ideally he would have liked to build a four-stroke, but MZ wouldn't let him. Next best was to build a 'split-cingle' two-stroke, like they had before invading Austria and Poland, when they were called NSU, but he wasn't allowed to do that either... so he set about looking at what he could do with the extremenly simple piston-ported RT125/Bantam engine.

The big issue was that with the piston sucking charge into the crank-case as it rose.... it had a habbit of shoving it all back out the way it had come, when it came back down. The only reason it didn't was because of curiouse flow effects making the charge better at flolwing one way than the other, so more went in, than came out.

Adding a disc valve to the system, doubled the potential power a two stroke could make in one go... but, then having got twice the charfge in the pot, with bloomin great holes in the cylinder wall, it was just as want to bugger off down the exhaust pipe, as stay there to get burned and push piston.

"Harmonic tuning" was Walter's answer; making an exhaust that deliberately hampered flow, so that all that preciouse charge didn't bugger off, but better still, using the noise waves so that when they were reflected, they shoved a chunk of escaped charge back in the pot.

THIS is what makes two stroke exhaust design something between rocket science and voodoo, and rather critical; to a 2T engine's performance....

What is removed from that DT spannie by fellow with an angle grinder is mesh.

It effects the critically calculated chamber cross section and volume very very little, but, it adds some wall resonance 'damping', to reduce the bottle amplifying exhaust noise like a megaphone.

Removing it will do bludger all for performance of the engine.

Chopping bluddy great sections of pipe out the bottle, and trying to weld them back in place, whilst not effing up that critical volume and section of the bottle? Yeah, might not effect engine performance much by not having the second skin in the bottle... but act of trying to remove that second skin PROBABLY will...

And you dont even have a welder?!?!?!?!?

Do you really think that this is a fantastic idea, to pigg off the neighbors with cutting discs coursing through steel, before making louder fart in a bean can noises every time you start the thing?
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[stevo as b4]

As said about, it's alot of effort for a sound change alone, and if you accidentally shorten the expansion chamber by slicing it open and re-welding it up, you could negatively effect performance.

If you want the noisy ringy tinging sound, buy a nice aftermarket performance pipe which will look better and be lighter, as well as maybe improving performance if you set it up right on a dyno.

If it's your daily ride to work at 6am then a quieter pipe might be more desirable. As does sometimes an aftermarket silencer on a std chamber, which often produces a louder but deeper sound than a thin single skinned expansion chamber which produces more noise than the silencer.