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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Pazon Sure Fire
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<blockquote data-quote="Tom Gaynor" data-source="post: 25454" data-attributes="member: 4034"><p>This comes from a separate discussion with David Dunfey, with the help of an article by Kevin Cameron, copies on receipt of private email.</p><p>Gilera and Honda multis, with a thin crescent section combustion space, ran advance of 55-60 degrees. "The burn" lasts twice the advance, so the mixture was still burning 55 deg ATDC. Nortons had much more efficient combustion chamber shapes, so ran 34 deg advance. (The Britton, and the legendary Harley racer "Lucifer's Hammer - wonderful name - ran something like 18 degrees advance.) IF twin plugs were doing any good, then advance would be reducing, because the mixture would burn faster. (This was my point when I started the thread "what advance do you run with twin plugs?" If it isn't LESS than with a single plug, the second plug is doing nothing. No one who answered ran significantly less. Ergo, twin plugs are a waste of time and money. I apologise in advance to anyone running, say, 34 with one plug, 24 with two, who didn't respond.)</p><p>So: the more advance one needs, the LESS efficient combustion is. If one is up to 43 degrees with twin plugs, take one plug lead off.</p><p>Another consideration is that electrickery is intrinsically lazy: if it is easier to fire one plug than the other, then that's where the current will go. If the "easiest plug" is not the best one from a combustion POV, then one will have to advance the timing <em>to accommodate a slower burn rate</em>.</p><p>Which means lower BMEP. Which means less torque. Which does not mean more power.</p></blockquote><p></p>
[QUOTE="Tom Gaynor, post: 25454, member: 4034"] This comes from a separate discussion with David Dunfey, with the help of an article by Kevin Cameron, copies on receipt of private email. Gilera and Honda multis, with a thin crescent section combustion space, ran advance of 55-60 degrees. "The burn" lasts twice the advance, so the mixture was still burning 55 deg ATDC. Nortons had much more efficient combustion chamber shapes, so ran 34 deg advance. (The Britton, and the legendary Harley racer "Lucifer's Hammer - wonderful name - ran something like 18 degrees advance.) IF twin plugs were doing any good, then advance would be reducing, because the mixture would burn faster. (This was my point when I started the thread "what advance do you run with twin plugs?" If it isn't LESS than with a single plug, the second plug is doing nothing. No one who answered ran significantly less. Ergo, twin plugs are a waste of time and money. I apologise in advance to anyone running, say, 34 with one plug, 24 with two, who didn't respond.) So: the more advance one needs, the LESS efficient combustion is. If one is up to 43 degrees with twin plugs, take one plug lead off. Another consideration is that electrickery is intrinsically lazy: if it is easier to fire one plug than the other, then that's where the current will go. If the "easiest plug" is not the best one from a combustion POV, then one will have to advance the timing [I]to accommodate a slower burn rate[/I]. Which means lower BMEP. Which means less torque. Which does not mean more power. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Pazon Sure Fire
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