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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modern Fuel & Ignition Advance
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<blockquote data-quote="davidd" data-source="post: 94885" data-attributes="member: 1177"><p>Pete,</p><p></p><p>I was starting with a twin plug BTH with electronic timing. The tuning was done at 7000 rpm. Although I don't know exactly where the advance should stop advancing, I understand that as the speed of the engine gets higher, the combustion becomes much more efficient. This efficiency means the advance is not necessary. I believe that test engines have run over 20,000 rpm with no extra advance necessary. </p><p></p><p>I could run fixed advance on the racer. I was getting 42 bhp at the rear wheel at 7000 rpm with the timing set at 19 degrees. On this engine I believe I started at 26 or 28 degrees and worked my way down, increasing power while reducing the timing every run. I mentioned 40 degrees above simply because so many owners seem to run a lot of advance.</p><p></p><p>What surprised me was that Cosworth promoted so much advance. It seemed to me that most tuners describe exactly the opposite, tuning for the most power at the most retarded position possible. </p><p></p><p>Much of this discussion is above my pay grade. I tried to figure out what the advance/retard timing curve should look like. I think that is an excellent question, but I could not find much on this subject. I was planning on switching the racer to a programmable ignition so that I might get some starting retardation that went to full advance prior to 19 degrees. That can be done easily now, but I think it is more important for street machines. I would guess that retarded timing might help a Vincent's performance up to 3500 or 4000 rpm, but it is a guess.</p><p></p><p>David</p></blockquote><p></p>
[QUOTE="davidd, post: 94885, member: 1177"] Pete, I was starting with a twin plug BTH with electronic timing. The tuning was done at 7000 rpm. Although I don't know exactly where the advance should stop advancing, I understand that as the speed of the engine gets higher, the combustion becomes much more efficient. This efficiency means the advance is not necessary. I believe that test engines have run over 20,000 rpm with no extra advance necessary. I could run fixed advance on the racer. I was getting 42 bhp at the rear wheel at 7000 rpm with the timing set at 19 degrees. On this engine I believe I started at 26 or 28 degrees and worked my way down, increasing power while reducing the timing every run. I mentioned 40 degrees above simply because so many owners seem to run a lot of advance. What surprised me was that Cosworth promoted so much advance. It seemed to me that most tuners describe exactly the opposite, tuning for the most power at the most retarded position possible. Much of this discussion is above my pay grade. I tried to figure out what the advance/retard timing curve should look like. I think that is an excellent question, but I could not find much on this subject. I was planning on switching the racer to a programmable ignition so that I might get some starting retardation that went to full advance prior to 19 degrees. That can be done easily now, but I think it is more important for street machines. I would guess that retarded timing might help a Vincent's performance up to 3500 or 4000 rpm, but it is a guess. David [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Modern Fuel & Ignition Advance
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