Brokenhead, I agree the oil probably is the same as it was "back then", but the cams in question are not! The designs have changed a lot over the years with fast ramp technology, higher lifts, much greater valve spring pressures, and even the material they are made from. If you are dealing with a true stock, old style engine, no high performance what so ever, then yes, the oils of today will be all thats needed.
When a oil type really matter is with a new high performance cam with much more lift, greater spring pressures, and fast ramps. These are the cams that need zinc. Comp cams Extreme Energy is a good example. In a cam cycle, 720 degree's, you only have so much room to get a valve open and closed. If you can slam the valve open as quickly as possible and slam it shut as fast as possible, you can increased the total valve open time considerably. Where as a slow ramp, such as used "back in the day", the valve was open just as long, but not open as much at each end of the cycle. It might takes as much as 30 to 40 degrees of rotation to get a old style cam lobe to .050" lift, where as todays cams can do it 15 or 20 degrees of rotation. It also takes a valve spring with a high spring rate to control that much lift in such a short amount of room, and along with that comes extreme lifter to cam contact pressure.
I am a firm believer in thin oil, I run a 5W20 in my 250, and Dad runs 5W30 in his 469 inch Pontiac, both synthetics. My local NAPA sells a 0 weight oil for some import cars! I just won't use one for break-in. I like mid weight oils, thick enough to hang on parts, but not so heavy it can't be thrown around.
Joe
