Quote:
Originally Posted by Mart
I might be wrong but overlap is something associated with performance engines. When I observe a flathead with a stock cam the exhaust closes then the inlet starts to open. They are not both open at a similar height at the same time.
But the bottom line is that the point at which the exhaust has just closed and the inlet is just about to start to open is the point at which the piston should be at TDC.
For reference, No.6 valves behaving as described above will coincide with No.1 at TDC having just fired. (On the firing stroke).
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Hey Mart, The intake opens just before the exhaust closes, so both valves are off their seats at the same time near TDC but only for a few degrees which is called overlap. The exhaust stroke is overlapping the intake stroke for a few degrees.
Good subject for a video on Mart's Garage.
Bill