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Originally Posted by bobcowan
As for the roller cam, unless you're putting in a huge cam, there's very little performance differance between roller and flat tappet. I think the test showed that l;ess than about 260* it's a wash.
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Not sure what test you saw, but the roller has a huge advantage in the rate at which you can open and close the valves. The flat tappet limit is due to the lifter starting to dig into the cam lobe, if the ramp rate is too high. A roller, at the exact same lift and duration as a flat tappet, will have the valve fully open sooner and can hold it open until later. This gives more flow and thus more HP.
Certainly someone could build a roller cam and not take advantage of this fact. A roller cam could be built to the exact profile of a flat tappet cam. Then if you compared that roller cam to the flat tappet there would be no advantage. However it is not possible to duplicate a well designed roller cam with a flat tappet cam.
The OHC 4.6 Ford is pumping out 240 - 260 hp out of 281 cid in family cars with very mild durration by taking advantage of the steep ramp rates possible.