Quote:
Originally Posted by Singleton
About the lifter oil hole being exposed. On all cams (that I’ve seen), the nose of the cam is at the same height relative to the cam journal. That is about .010” below the cam journal radius (see pic of stock cam). (Can’t be higher than the journal or the cam wouldn’t fit into the block). So the lifter will rise to the same height regardless of lobe lift. The smaller the base circle, (more lobe lift), the more chances of the lifter oil hole being exposed at the bottom of the lifter bore.
Put another way, comparing two cams, one with .300 lobe lift, and one with .350 lobe lift. Both lifters will top out at the same place, but on the .350 cam the lifter starts out .050 lower in the lifter bore.
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The OD that the cam profile is ground on, and its effect on the base circle will vary more than you might expect. I have seen the lobe .050” (.10” smaller dia, 1.797” on a 1.897” cam bearing journals), and with in .005” (.010” Dia) 1.885” on a 1.897” cam tunnels. I mocked 2148s several years ago in several blocks with different cams, one of them exposed the oil hole .030”, out the top and nearly exposed the bottom band also. Each grind and mfg is going to be a bit different. I think an “S” journal lobe’s OD should end up .010” smaller than a “B”, but I am not totally sure on that I recall it can effect the base circle.