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Posted by chris case [63.199.243.158] on Thursday, June 21, 2012 at 15:17:07 :
In Reply to: Re: Flat heads can't get more lift. posted by Dave K. Royal [75.81.249.81] on Thursday, June 21, 2012 at 00:13:00 :
Both valves are actually closed for several degrees, instead of an 'overlap' where both are open for several-to-lots degrees.
During overlap, the exhaust gasses exiting make a suction and pull in some intake gasses. With the real benefit being it gives the intake charge added momentum, lots more can get into the cylinder.
The lack of overlap is why a flathead runs at such low speed- I had one idling at 50 rpm, not enough to make oil pressure. Also why they make such poor power up high.
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