Silencer Design

[Turbo-Brown]

Does anyone know what aspects of silencer design affect the amount of noise that comes from the tailpipe?

I've got a giant single straight through can at the rear of my exhaust but I have no idea whether I should pack the silencing material in tightly or loosely, and also I have no idea whether halving the volume of the can will make the exhaust twice as loud (which is also an unknown quantity).

I don't want the car to be too loud, but a bit of a gargle wouldn't go amiss

Any help hugely appreciated as always!

Cheers!

Alex

[kam-325i]

Having worked for an exhaust manufacturer for a few year's, i think i can make a comment.

There are two basic methods: Wadding packed or Baffled.

In the wadding design, a glass fiber/ceramic material is used to absord the sound energy from the exhaust.

in the baffle design, which is less restrictive, the pipe that brings in the exhausts into the silencer only enters the silencer for about 30/40%. the end is capped, and the walls perforated. the idea is to make the sound energy bounce around the inside of the silncer a few times to absorb some of the energy so by the time it exits, it has lost around 80% of its entry energy.

[Turbo-Brown]

Hokey doke, cheers for the quick reply

I've got two straight through perforated pipes which enter at one end and exit at the other to atmosphere.

Plan is to pack the can with ceramic wadding but I'm still a little unsure how much of the stuff I need to pack in there

[kam-325i]

you need to make sure the perf pipes in the silencer are blocked in the main bore / ID. this is so that the sound energy does not have a straight route to the outside atmosphere(sp)

The way it works is like this. as the exhaust enters the silencer, i has lots of sound energy, by making the "sound" bounce around inside the silencer looking for the exit, it lose's some of that energy and sound's quiter.

[Turbo-Brown]

Hokey doke, many thanks for the advice

Think I'll run it straight through to start with and see how loud it is (I gather that turbos act as pretty good silencers. If it's too noisy, I can make up a couple of plugs to shove into the perforated tubes so the gas has to travel through the silencing medium

Cheers!

Alex

[ndg]

By the sounds of it you have a can designed to run straight through. If you you try to baffle the perf pipe and put wadding in you'll strangle the engine.

Silencer design is very complex, and to do a proper design you need to either experiment alot or use some fancy design software(totally unavailable unless your a big company or university! A perfect silencer wound not slow the gas down at all but would remove all pressure pulsations from the gas(from the individual cylinders). Even with the straight through design you can put a baffle in the wadded area only to give you 2 seperate silencers in the same box tuned to different frequencies.

But to start with I would suggest just packing the muffler firmly and trying it. As you say Turbos do a good job of silencing the exhaust noise anyway, so it may be fine as is.

I've got two small parallel silencers on a classic car running a 2.5l straight six(not BMW) and they are fairly loud, but with a large can, turbo, and the E30 being quite a bit bigger(exhaust is further from your ear) you should get some satisfactory results to start with.


Nathan

[Turbo-Brown]

Not a Triumph of some description is it?