I have an engine with a flat tappet cam that likes high zinc and phosphorus but it also happens to be high mileage. There are few oils out there that offer high zinc/phosphorus AND all the other high mileage oil benefits, especially without paying alot of $$$. Additives can be used to boost certain things but without some thought on it, it can sometimes do more harm than good. Your opinions on oil brands and the use of additives aside, I'm curious on how the math works out. Lets say I have 4.25qts of Mobil 1 High Mileage 10W-40. According to the following link it has 1100ppm of zinc and 1000ppm of phosphorus. Mobil 1 - Zn/Ph Content Already its a pretty good oil. But lets say for arguments sake my particular engine needs a bit more zinc and phosphorus. Lets say I want to add an off-the-shelf ZDDP package. Lets use Rislone's Concentrated Oil Supplement w/Zinc as an example. Rislone Concentrated Engine Supplement The bottle is 11oz and the datasheet says it has zinc content of 1.56%. Can someone show me the math of how adding the 11oz bottle of the Rislone Zinc additive to 4.25qts of M1 HM will effect zinc levels in PPM? I would appreciate it! Thanks!