[David Hodgson]

Hi Mark,

Chris and I did a fair bit of experimentation back in about '98 on quitening pipes, even tried the full 4" spiral type with no glass packing through to what Rob pic's are. I found there was the louvered tube, perf tube with large holes (4.5mm?) but less of and perf tube with say 2.5 or 3mm holes but many of. This last one was by far the most successfull. The full spiral type were a messy sound.

I ended up using exactly what Rob has pictured with the spiral washers on the 20mm tube inside the fine perf glass wrapped pipe for rego with a bit of extra steel wool. I replaced the 20mm tube with a length of booker rod and kept staggered spiral washers, but for the entire length of the pipe. I think it got it down around 100db, but mine is only a low comp 302 with 2" tube.

I figure the key was to interfere with the nose/centre of the sound wave. With straight through tube this does not happen - the front of the sound wave is free to travel right through uninterupted.

I originally tried two 15 or 18 inch round perf mufflers with a 3" chamber between them. I thought this idea would be great but was no good. Probably needed a small baffle in the centre chamber.

Rob, that is so uncanny - the pic with the tube is almost identical to mine. My washers have clearance between them and the tube, and was supported in the tube by a disc with holes at each end. Got me through rego but really choked above 3500revs.
I'm going to have to test it again as mine has been out of rego for more than 12 months and in ACT it will need to go over the 'pits' again.

The Summit cone looks interesting, when I have mine apart for rego I might try something like it.