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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Blind jetting
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<blockquote data-quote="davidd" data-source="post: 96877" data-attributes="member: 1177"><p>It is very difficult to get the exhaust to work correctly. It starts at the exhaust port, which is a bad design. It is very restrictive, which makes the Vincent not very sensitive to jetting changes. I asked Marty Dickerson once what jetting he used at Bonneville compared to what he used at Daytona (4000' difference) and he said he used the same jetting because it did not make any difference. When Carleton had his head flowed the first thing he found on the dyno was that changing a jet one step could get him more than a horsepower. That never happened before the head work. Before when you changed the jet it could get you a different color plug, but there were never any big spikes in HP. </p><p></p><p>The Vincent does amazingly well with big straight pipes. These are very lazy about evacuating the combustion chamber. The exhaust charge in a two inch pipe leaves with a snail's pace, but that seems to be OK with the exhaust port so restricted. The engine makes very good power low down. </p><p></p><p>If you are trying to compete with others, the only thing you can do is to increase the RPM's, otherwise, they walk away from you. You can cut the 2" pipes back to 28" or you can go to a smaller diameter and add a few inches (1-3/4" = 31"). These are just targets and they have to be tuned in. Irving said you could pick a short pulse to tune in on and then double it and that would work. I believe this is how he came up with the lengths used on the racers. I was unable to do that. My doubled straight pipe made the bike slower. This work was so expensive and time consuming that I could not do a lot of it.</p><p>[ATTACH=full]22576[/ATTACH]</p><p>Steve Hamel's 2" pipes are about the same 28" length and Steve has done a ton of dyno work. I believe this bike showed 124 BHP on the dyno.</p><p></p><p>I was revving my bike to 7000 rpm on the dyno. I suspect Steve was also as he told me that he could run up to 9000.</p><p></p><p>It is always interesting to see what the experiments of others yield.</p><p></p><p>David</p></blockquote><p></p>
[QUOTE="davidd, post: 96877, member: 1177"] It is very difficult to get the exhaust to work correctly. It starts at the exhaust port, which is a bad design. It is very restrictive, which makes the Vincent not very sensitive to jetting changes. I asked Marty Dickerson once what jetting he used at Bonneville compared to what he used at Daytona (4000' difference) and he said he used the same jetting because it did not make any difference. When Carleton had his head flowed the first thing he found on the dyno was that changing a jet one step could get him more than a horsepower. That never happened before the head work. Before when you changed the jet it could get you a different color plug, but there were never any big spikes in HP. The Vincent does amazingly well with big straight pipes. These are very lazy about evacuating the combustion chamber. The exhaust charge in a two inch pipe leaves with a snail's pace, but that seems to be OK with the exhaust port so restricted. The engine makes very good power low down. If you are trying to compete with others, the only thing you can do is to increase the RPM's, otherwise, they walk away from you. You can cut the 2" pipes back to 28" or you can go to a smaller diameter and add a few inches (1-3/4" = 31"). These are just targets and they have to be tuned in. Irving said you could pick a short pulse to tune in on and then double it and that would work. I believe this is how he came up with the lengths used on the racers. I was unable to do that. My doubled straight pipe made the bike slower. This work was so expensive and time consuming that I could not do a lot of it. [ATTACH=full]22576[/ATTACH] Steve Hamel's 2" pipes are about the same 28" length and Steve has done a ton of dyno work. I believe this bike showed 124 BHP on the dyno. I was revving my bike to 7000 rpm on the dyno. I suspect Steve was also as he told me that he could run up to 9000. It is always interesting to see what the experiments of others yield. David [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Blind jetting
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