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General Chat (Vincent Related)
Valve Timing
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<blockquote data-quote="davidd" data-source="post: 115969" data-attributes="member: 1177"><p>Andrews did recommend splitting the overlap. I usually think of this in terms of the "cross over point", that is, the point where the exhaust valve and the intake valve are precisely the same height. Vincent put this point at 4 degrees BTD. Andrews recommended 0 degrees, or 4 degrees different. The bikes will run at either position and it may be difficult to note the performance difference. I am not certain that Andrews offered that advice after dyno testing a Vincent. I suspect not. Vincent did dyno testing, but their 4 degree spot was based on running engines that were built to a very standard spec.</p><p></p><p>I know you can advance or retard that "cross over point" and get different performance as you say. I am not certain that the window of movement is very large. That window will depend on the height of the piston and the lift of the cam. Often, the cross over point is shifted simply to keep the valves from hitting the piston.</p><p></p><p>David</p></blockquote><p></p>
[QUOTE="davidd, post: 115969, member: 1177"] Andrews did recommend splitting the overlap. I usually think of this in terms of the "cross over point", that is, the point where the exhaust valve and the intake valve are precisely the same height. Vincent put this point at 4 degrees BTD. Andrews recommended 0 degrees, or 4 degrees different. The bikes will run at either position and it may be difficult to note the performance difference. I am not certain that Andrews offered that advice after dyno testing a Vincent. I suspect not. Vincent did dyno testing, but their 4 degree spot was based on running engines that were built to a very standard spec. I know you can advance or retard that "cross over point" and get different performance as you say. I am not certain that the window of movement is very large. That window will depend on the height of the piston and the lift of the cam. Often, the cross over point is shifted simply to keep the valves from hitting the piston. David [/QUOTE]
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