Some of this has been blown totally out of proportion and is unecesarrily alarmist.
Another factor that has not been discussed here is the fact that for a while there were a bunch or very poorly made tappets being sold. There was a glut of cheap asian produced solid lifters that flooded the market a few years back (2000-2001) and caused all sorts of cam failures that had nothing to do with the oils used. This was not only a problem with our cars but hit the muscle car crowd pretty hard as well. The muscle car crowd uses solid lifters in their very hot street and race motors. Otherwise most of them have switched over to hydraulic lifters for the majority of applications.
The problem of bad lifters has been pretty much worked out. I have personally seen two sets of bad lifters (one set being in my own engine). In both cases that I witnessed the lifters/tappets were replaced with higher quality items that were tested for appropriate hardness (Rockwell) before sale. In both cases I witnessed, the lifter began to disintegrate but the cam lobes were completely unharmed.
The reduction in zinc levels in oils can have an effect on the ultra high performance engines with very radical lift cams and the resulting higher pressures they develop at the cam/lifter interface. Castrol has stated publicly that their oils, especially 20W50, are fully backward compatible and more than meet the needs of solid lifter engines that are still primarily as the manufacturer intended. They also say that current oils are tested to a higher degree than older oils which adds to their confidence that their modern oils are just fine in our old technology engines. So they are saying that stock engines should have no fear of the reduced zinc levels. (As long as the rest of the internal engine parts are up to snuff, but that is not the oil companies problem)
Really, any of our cars that are still streetable, even with higher lift cams, should encounter no problems. Engines built with truly radical camshaft lift numbers, essentially cams designed for racing, should use oils designed for racing as they still contain the appropriate levels of zinc. If you are feeling especially worried about it then you can also use racing oils in your street car to maintain those levels of zinc or add some cam break in lube with every oil change. Though the effectiveness of the latter is debateable as to just how much the break in lube can mix with the oil and provide a consistent form of protection.
The reason zinc levels have been reduced is that they have found the zinc to have a detrimental effect on catalytic converters and thus the content of engine oils become a contributing factor in emissions. Several diesel oils still contain zinc but they are slated to cut back on zinc content as well again due to tightening emissions regulations. Which will eventually leave racing oils as the only oils available that do not have to worry about the emissions ramifications.
Bottom line, good old Castrol 20W50 should still serve well with no problems. But if you are worried, then by all means use Racing formula oils, some diesel oils will work just fine as well or try adding some cam break in lube with each oil change. Peace of mind can often be worth the extra money.
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