Perforated tube

[Alley Kat]

99% sure the packing they sell for exhausts is just a fibreglass wool.

Not sure of tube sizes etc now - modded old cans, so the tube matched the tailpipe end inside the can (they were resonators, chopped that stuff out, made st-thru)
Holes quite large, 4-5mm or so, not yer tiny ones - pillar drill was dead at the time so all hand power drill - bigger meant less work. Maybe lots of small ones is better? No idea.




Wee hole in the end stub was in case of needing to add a baffle for MOT... thinking dirt cheap Beetle baffles, steel tube type. Never needed to though.

[topcatcustom]

'Ere we go! Made for 2 1/2" internal tube: http://www.cbsonline.co.uk/6-silencer-w ... -434-p.asp

Looks like I'm back on for making me own mufflers!

[katanaman]

I would just go with the fibre and forget the stainless. Have look round bike supply places as its common place on bikes to pack exhausts but car its a bit more exotic re expensive!

[topcatcustom]

After a measure up I only have 400mm of length for the silencers, if I go ahead with my straight throughs will that short length actually do anything for getting the db's down? There is loads more width under the boot but that would mean more bends etc, the only other option is to go with turbo mufflers that arent straight through.

[Ian Anderson]

400mm is a luxury!

Yes it will make a huge difference

IAn

[Alley Kat]

It depends ...
You can pack it denser/lighter
The diameter outside the central tube makes a difference.
The size/spacing of holes in the tube too.

My bike ones above only had about 15cm of packed chamber, and that was quite loose.

Ideally don't finish weld it up, test it out first. There is no way of knowing what it'll be like without actually running them, with the variables of packing, diameter etc.

I've just modded some full-length bike ones, drilled the resonators out. Expecting much noise as they've got a straight through path with no glasspacking now, but they're quite liveable with.

[topcatcustom]

I found some perforated sheet at work (2mm with 3mm holes, approx 40% spacings so quite "open") which I will roll into a 2 1/2" tube. I was going to roll some 6" dia tube for the outer cans which will give 1 3/4" packing all round, if too loud could I put some semi circular baffles in on a removable slide?

And I'm assuming the less packing (or less dense), the quieter it gets as more air space to fill?

[Ian Anderson]

Or run some supertraps / add in silencers on the tail pipes for the test

Kills power output but will keep the tree huggers happy


Ian

[Alley Kat]

I think less dense=noisier, less glass killing the sound waves.
On cans above I left provision to slide in Beetle baffles, inside the central perf tube, but didn't need them although the noise got a mention on the MOT. Or can make some, more perf tube, hammer the forward facing end into a point with three or four fold lines.

[kiwi303]

if you want to bend your holey tube why not use a modification of the ice crush method? when bending solid tube on a hydraulic bender, bending empty tube can crush in the inner side of the tube and narrow the effective inner diamensions of the tube. A way to avoid that is to plug one end and fill it with water then freeze standing up so the ice can expand up the tube as it freezes, (don't plug both ends, you can split the tube). Bending that on a hydraulic bender now means the ice fills the tube and resists the crushing forces keeping the tube nice and round...

Just find a soft plastic pipe or water balloon that will fit down the perforated pipe and fill it with water...