[track73]

When I started building engines 50 years ago I always used the cam opening and closing events @ .050 lift to degree a cam. My engines always ran great. what was I missing in all these years by not using the intake centerline method?

[Skip Fix]

That will usually get you right on. Some asymmetrical cams like Ultradynes lobes(and I think the Lunati VooDoo also designed by Harold Brookshire) recommend the centerline method to get the centerline right on. But you would think they would still have the data for the correct 0.050 lift numbers for their lobes.

[70GS455]

Originally Posted by Skip Fix

That will usually get you right on. Some asymmetrical cams like Ultradynes lobes(and I think the Lunati VooDoo also designed by Harold Brookshire) recommend the centerline method to get the centerline right on. But you would think they would still have the data for the correct 0.050 lift numbers for their lobes.

Some do some don't. Believe it or not, for an assymetrical cam, what's printed on the cam card and even the little program they use to determine the 0.050" opening and closing events do not take into account that the lobe is asymmetric: they just assume the lobe is symmetric and that those numbers are "close enough". In order to determine the correct opening and closing points, they have to go into the cam file and manually look at the 0.050 numbers. This was what I was told by company "B" and company "CC".

It's easy enough to check. If you know your lobe is symmetric, it's a trivial calculation: half of the lobe falls on either side of the centerline. If you know your lobe is assymetric, you can check if they cheated in giving you close enough numbers: they will agree with the assymetric calculation.

One comment on what constitutes "centerline". For an assymetric profile the center of the upper lift area, the center of the opening and closing events, and the center of the total lobe area do not all equal the same thing.

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[Vid]

My Ultradyne cam card, among the usual specs, also shows duration at .006. Not really sure why they provide that particular measurement.


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