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Pete · 07-29-2010, 12:38 PM

"could be beneficial in not exposing the edge of the lifter to the camshaft lobe lifting ramp in the most radical racing cam designs. "

That doesn't happen in any cam I have ever seen...It may appear to but actually does not touch the edge...If it did the cam and lifter would be toast in a short time.
The reason for using a larger diameter cam blank in a flathhead is because at anything over .420 lift on a stock core you can't get the cam in the block..To get "more cam" you need to increase the lift along with the RATE OF LIFT...On the Isky 505A and several other manufacturer's cams with more lift they either run the cam in the block or bore the cam line and put inserts in.
It is possible to design a cam with a rate of lift so high that on a graph the accelleration curve would be a vertical line..This would require spring pressures so high in order to work that the system would fail mechanically.
Isky found that .011 per degree squared was the practical limit for the 505A...In order to get more it would require an inverted flank acceleration ramp..That is not practical with a radius lifter....Many modern roller lifter racing cams have inverted flanks but they require spring pressures that are hard to imagine....In some cases 800 lb on the seat..1200 open...The springs are 2 inches in diameter, have 3 coils and are made from 5/16 diameter wire.

07-29-2010, 12:38 PM	#60
Pete Senior Member Join Date: May 2010 Location: Wa. Posts: 5,408	Re: Boring a flathead "could be beneficial in not exposing the edge of the lifter to the camshaft lobe lifting ramp in the most radical racing cam designs. " That doesn't happen in any cam I have ever seen...It may appear to but actually does not touch the edge...If it did the cam and lifter would be toast in a short time. The reason for using a larger diameter cam blank in a flathhead is because at anything over .420 lift on a stock core you can't get the cam in the block..To get "more cam" you need to increase the lift along with the RATE OF LIFT...On the Isky 505A and several other manufacturer's cams with more lift they either run the cam in the block or bore the cam line and put inserts in. It is possible to design a cam with a rate of lift so high that on a graph the accelleration curve would be a vertical line..This would require spring pressures so high in order to work that the system would fail mechanically. Isky found that .011 per degree squared was the practical limit for the 505A...In order to get more it would require an inverted flank acceleration ramp..That is not practical with a radius lifter....Many modern roller lifter racing cams have inverted flanks but they require spring pressures that are hard to imagine....In some cases 800 lb on the seat..1200 open...The springs are 2 inches in diameter, have 3 coils and are made from 5/16 diameter wire.