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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
poor quality repop silencers
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<blockquote data-quote="druridge" data-source="post: 88117" data-attributes="member: 3754"><p>There are formula on the internet for calculating exhaust lengths; most folk use maths by A Graham Bell, I grew up with maths by Phil Irving, I thought this must have been from Tuning for Speed but I now cant find it.</p><p>I was shown an interesting way to check the tune of a pipe length with a cigarette paper. We were playing with the straight through exhaust on a single on the beach at Kirk Michael (IOM). I seem to remember it was Dave Taylor (stunt rider etc) who showed us how to slide one piece of straight pipe over/along another slightly smaller bore pipe (eg the down pipe) to find the position at which the gas 'wave' (?) exits with least turbulence. This length starts as a function of the distance from end of bellmouth to back of the inlet valve. From memory if this was eg 7", you would start looking for this low turbulence point at eg 49" (7 x 7"), I cant remember why. This point is altered a bit by revs, but if the length is wrong, at your chosen revs the paper is torn to bits, at the point where the length is correct the paper just waves about in the exhaust gas. At this point the motor seemed out smooth out, calming vibration and improving the exhaust note. I dont know if this point also produce the most power but the bike felt good. I recall its a good idea to tune the pipe length to match the revs where the engine is going to spend most of its time. On some singles the downpipe protrudes well into the silencer so its quite easy to fine tune this length. I've never tried but its hard to imagine this cigarette paper working on a twin?</p></blockquote><p></p>
[QUOTE="druridge, post: 88117, member: 3754"] There are formula on the internet for calculating exhaust lengths; most folk use maths by A Graham Bell, I grew up with maths by Phil Irving, I thought this must have been from Tuning for Speed but I now cant find it. I was shown an interesting way to check the tune of a pipe length with a cigarette paper. We were playing with the straight through exhaust on a single on the beach at Kirk Michael (IOM). I seem to remember it was Dave Taylor (stunt rider etc) who showed us how to slide one piece of straight pipe over/along another slightly smaller bore pipe (eg the down pipe) to find the position at which the gas 'wave' (?) exits with least turbulence. This length starts as a function of the distance from end of bellmouth to back of the inlet valve. From memory if this was eg 7", you would start looking for this low turbulence point at eg 49" (7 x 7"), I cant remember why. This point is altered a bit by revs, but if the length is wrong, at your chosen revs the paper is torn to bits, at the point where the length is correct the paper just waves about in the exhaust gas. At this point the motor seemed out smooth out, calming vibration and improving the exhaust note. I dont know if this point also produce the most power but the bike felt good. I recall its a good idea to tune the pipe length to match the revs where the engine is going to spend most of its time. On some singles the downpipe protrudes well into the silencer so its quite easy to fine tune this length. I've never tried but its hard to imagine this cigarette paper working on a twin? [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
poor quality repop silencers
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