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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modern Fuel & Ignition Advance
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<blockquote data-quote="LoneStar" data-source="post: 95413" data-attributes="member: 585"><p>Martyn,</p><p></p><p>This was one of the inspirations for my original post, in that the figures are given without a discussion of how they were arrived at. It's said that modern fuel is the relevant factor, suggesting it burns faster than when the factory specified 39 degrees, but no one here seems to know why or to what extent (despite a great deal of informative technical discussion on ignition advance). </p><p></p><p>Assuming a standard Vincent twin, with compression ratio in the range the factory used (6.7 - 8:1) and original magneto/ATD, fuel composition is the only factor I can think of that would invalidate the factory's original specification. To see if it does, we could look at fuel burn characteristics (seemingly unavailable) or dyno tests on actual standard bikes running various fuels (race gas, pump unleaded, maybe some leaded premium if available) - but it seems no one has done this either.</p><p></p><p>Lacking hard data, we can fall back on "it seems to run best at x degrees" - but as davidd points out, seat-of-pants impressions are notoriously unreliable.</p></blockquote><p></p>
[QUOTE="LoneStar, post: 95413, member: 585"] Martyn, This was one of the inspirations for my original post, in that the figures are given without a discussion of how they were arrived at. It's said that modern fuel is the relevant factor, suggesting it burns faster than when the factory specified 39 degrees, but no one here seems to know why or to what extent (despite a great deal of informative technical discussion on ignition advance). Assuming a standard Vincent twin, with compression ratio in the range the factory used (6.7 - 8:1) and original magneto/ATD, fuel composition is the only factor I can think of that would invalidate the factory's original specification. To see if it does, we could look at fuel burn characteristics (seemingly unavailable) or dyno tests on actual standard bikes running various fuels (race gas, pump unleaded, maybe some leaded premium if available) - but it seems no one has done this either. Lacking hard data, we can fall back on "it seems to run best at x degrees" - but as davidd points out, seat-of-pants impressions are notoriously unreliable. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modern Fuel & Ignition Advance
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