ZddPlus is formulated for use in older engines with flat tappet cams-----it will raise the Z&P levels of newer SM rated oils to slightly under 2000PPM with an average oil change of around 5 quarts-------this concentration will put the protection level of SM oil on a par with full blown racing oil--------it is not really necessary for roller tappet engines unless the engine has very stiff valve strings like are typically found in high RPM/high powered engines-------there are some reasons to use it in some engines but that must be tempered with the shortened life that may result to the "catastrophic" convertor---------zddp improves the lubrication ability of oil whenever there are rubbing steel or iron surfaces that do not have the benefit of pressurized lubrication-------ie rockers, pushrods, wrist pins, timing chains etc................RC
