I run it in my 1958 Ford which uses 10W-30 oil as the zinc is too low for a flat tappet motor.
Some background: beginning in the 1990s, the American Petroleum Institute (API) began having oil companies reduce the zinc levels in 10W-30 motor oils. The reason is that zinc is detrimental to catalytic converters.
However zinc is needed for old style motors with rocker arms and traditional camshafts (called "flat tappet" in that industry). So car companies began to convert to "roller tappet" valve trains as a way around the lack of zinc.
These lowered zinc levels only apply to 10W-30 oils, according to the API. For older motors, adding ZDDP+ per oil change takes care of the problem.
10W-40 and 20W-50, more popular for motorcycles, are not affected. In fact Valvoline 20W-50 Racing Oil has excellent zinc levels suitable for classic motorcycles such as CB750s. I recently ran into Castrol 20W-50 Motorcycle Oil and suspect it is equally good or close. Right now I am running the Valvoline in the CB750 I just rebuilt.
John
