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News and On This Day
David Tompkins Vincent at Daytona
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<blockquote data-quote="greg brillus" data-source="post: 150162" data-attributes="member: 597"><p>The Vincent engine is a good strong design, but not an easy one to easily get big HP from........the basic issue with most all these old engines is the relatively primitive cam/valve train design. This coupled with the combustion chamber shape, and low port angles does not help........Running a good twin in even basic tune will be a winner, only due to the shear cubic inches alone........The downside is the massive weight.......An average twin even with many parts removed and lightened were possible is still nudging 90 odd Kg's just the engine unit........The big downside to this in racing is stopping it. The opening and closing of the valves is were it matters most........having massive duration big overlap cams seem great but the big downside is the huge loss in compression........I'm sure in my engine this is where i'm loosing out.........The cams and followers are very , very small, and so once you hop things up, the load on them goes through the roof.........This is probably the biggest weekness in a Vincent for getting bigger power gains........You need to snap the valve open quickly, hold it open for as long as possible, then snap it shut........with our valve trains, this is very difficult........A weak supply of oil delivery here will not help........ Symetrical race cam lobes, roller followers, and ratio rockers is the answer.......But then you need much stronger valve springs to cope.......lighter valves and other parts are a must........This is all known stuff.......The Horner brothers use this exact spec on all their engines........but it is mostly beyond all of us without very deep pockets or a full CNC machine shop like they do.........I am trying to do some but not all of these mods, in an effort to get some gain.........My ultimate gain would be to make the roller followers and symetrical cam set up........That would give the best gains I feel.......Making it all survive is another thing, so beefing up the entire valve train is the only way.</p></blockquote><p></p>
[QUOTE="greg brillus, post: 150162, member: 597"] The Vincent engine is a good strong design, but not an easy one to easily get big HP from........the basic issue with most all these old engines is the relatively primitive cam/valve train design. This coupled with the combustion chamber shape, and low port angles does not help........Running a good twin in even basic tune will be a winner, only due to the shear cubic inches alone........The downside is the massive weight.......An average twin even with many parts removed and lightened were possible is still nudging 90 odd Kg's just the engine unit........The big downside to this in racing is stopping it. The opening and closing of the valves is were it matters most........having massive duration big overlap cams seem great but the big downside is the huge loss in compression........I'm sure in my engine this is where i'm loosing out.........The cams and followers are very , very small, and so once you hop things up, the load on them goes through the roof.........This is probably the biggest weekness in a Vincent for getting bigger power gains........You need to snap the valve open quickly, hold it open for as long as possible, then snap it shut........with our valve trains, this is very difficult........A weak supply of oil delivery here will not help........ Symetrical race cam lobes, roller followers, and ratio rockers is the answer.......But then you need much stronger valve springs to cope.......lighter valves and other parts are a must........This is all known stuff.......The Horner brothers use this exact spec on all their engines........but it is mostly beyond all of us without very deep pockets or a full CNC machine shop like they do.........I am trying to do some but not all of these mods, in an effort to get some gain.........My ultimate gain would be to make the roller followers and symetrical cam set up........That would give the best gains I feel.......Making it all survive is another thing, so beefing up the entire valve train is the only way. [/QUOTE]
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David Tompkins Vincent at Daytona
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