advise on exhaust wadding

[hough]

hi im making my own exhaust box, cos i want some thing abit different to everyone else, but can any one tell me, what can you use as wadding, i understand you can use wire wool but what is better fibre glass wadding of stainless steel wire wool???

 

[obi_waynne]

Stainless steel wire wool is pretty good and is probably cheaper than glass wadding.

Fibreglass is better at damping the sound compared to wool.

A lot of the pros stick with wire wool but some performance shops are selling glass fibre matting.

What are you aiming at? Do you want much noise? How large is the silencer area to be packed?

I've heard that wool needs repacking every few years.

If you use fibreglass chopped srand matting you need to wash it first to rinse out the stuff that keeps it in a mat.

 

[hough]

the silencer is a cylinder 150mm dia by 360mm long with a bore of 71mm straight tho, all 316 stainless i just want to be different and want the best i can get as im a welder/fabricator so i got the tools anf the know how with the welding/making of the box

 

[obi_waynne]

How much do you know about exhaust silencer designs? This sounds like a fun project. I take it you are more worried about sound than performance then?

The only note i'd give on performance is to avoid a step in the pipe, different lengths should be joined by a cone shape and you should avoid bends as much as possible.

The elementary and really clunky theory for a straight through exhaust. Your 71mm bore will have holes along it, the sound waves travel through these holes through the deadening material, are then reflected back off the walls of the 150mm cylinder and become out of phase thereby cancelling the noise of the main stream of the exhaust.

The space between the exhaust main bore and outside makes the biggest difference to the sound. Initially I'd leave things open so you can adjust the packing to suit rahter than trying to get it right on the first go.

 

[hough]

i know a little bit about silencer designs, but not to sure how larger perforations effects the flow of gas as im using 6mm peforated sheet the whole lenght of the tube, as for the sound of the pipe my aim is for a nice deep rumble from my bmw 328i, i used to make silencers for tractors years ago using mild steel but have been trying to find out about sound waves...

 

[obi_waynne]

I'll admit it's far from my area of expertise. most exhaust use the 5mm perforations, I think the external bore to internal bore ratio has more to do with the sound. You can further deaden the sound with an expansion box just after the cat if you need to.

 

[hough]

thanks for your help, think i might have found a local motor bike centre that sells exhaust wadding, i will have to take pictures of this project and hope it comes out ok, even if the box sounds naff at least it will look good in a mirror finish.....

 

[T9 man]

Look forward to those pics! can't say I know off anyone who has actually made a silencer before

 

[obi_waynne]

A writeup in our DIY section would be awesome if you feel up to it! I'm sure it will help loads of people out.