I'm not totally surprised by the result. Presumably these race cans are simple absorption type 'silencers' with a perforated tube surrounded by packing. I'm sure Pip has had success with this strategy, but I wouldn't have thought just a 'twirl' would achieve a great deal as it's not actually increasing the area for absorption IYSWIM. TBC may be able to confirm whether it would significantly slow the speed of passage of the exhaust gas slug or not. Too much like proper fizziks for me. It would certainly have passed the old police noise test at Mallory in the old days. A copper on duty at the car park exit would pull over particularly noisy bikes and stick something akin to an army officer's swagger stick [1] up your reverse cone mega. If it hit something you passed, if not you were in trouble. The extra bit on the Nordwest's FPM race can also significantly reduced the outlet diameter and had a short length of pipe with a blanked off end and several holes drilled in it. Probably a bit like the db killers you already have I suspect. It made a huge difference to the noise level. It also significantly fucked up the gas flow unfortunately. I never bothered to get the jetting right for the road. although it was OK if you didn't give it a big handful at low revs in a high gear. I found that, as Frigerio had predicted it went so much better without it. The silencer on my old SWM achieved extra efficiency by having two perforated pipes in the muffler (and two outlets). Which reminds me that I recently found it in the shed and must list it on Ebay. [1] No connection with the 'cock' joke on 'First Light' last night. Looks not that unlike a wooden drumstick. I still have my father's in the loft. -- +-------------------------------------------------------------------+ | Pete Fisher at Home: | | Voxan Roadster Yamaha WR250Z/Supermoto "Old Gimmer's Hillclimber" | | Gilera GFR * 2 Moto Morini 2C/375 Morini 350 "Forgotten Error" | +-------------------------------------------------------------------+
They are indeed. I couldn't figure out how it would work, but as you say, it seems to have done so for Pip. I believe he said a 'perceived' reduction in sound though, so don't know if he ever measured the results. I'm sure he'll be along at some point. No, they're just smaller bits of straight through pipe with a flange round the outside to stop the gasses sneaking past. They knock 3db off so quite effective. I've tried putting a bit of flat bar sticking out the end & bent over[1] to stop the gasses having 'line of sight', which knocked another 1db off. I'm trying to get this sorted so I can book it in for a dyno session to map the PCIII. I'd be happy with 98db at 5k as that opens up more scope for trackdays. Should be able to do that without screwing up the gas flow with a bit more tweaking. [1] I mean the flat bar's bent over, not me.
Using the patented Mavis Beacon "Hunt&Peck" Technique, Krusty <http://www.bedtimeheaven.co.uk/subcat-cat~7-subcat~9-paging~-order_by~-o ffset~0.htm> HTH.
IME most RSMs in the (Australian) army had two swagger sticks -- the second was ramrodded up their arse! The one who didn't was a lovely chap and a good teacher -- and died of malaria in Vietnam. -- Ivan Reid, School of Engineering & Design, _____________ CMS Collaboration, Brunel University. Ivan.Reid@[brunel.ac.uk|cern.ch] Room 40-1-B12, CERN GSX600F, RG250WD "You Porsche. Me pass!" DoD #484 JKLO#003, 005 WP7# 3000 LC Unit #2368 (tinlc) UKMC#00009 BOTAFOT#16 UKRMMA#7 (Hon) KotPT -- "for stupidity above and beyond the call of duty".
