Shell reduced the ppm of ZDDP a few years ago. It was at one time 1600, then went to 1400 or so and now is 1200 (give or take...some weights are more like 1000ppm) I've read. There are better options if you want more ZDDP. Valvoline VR-1 still has 1400 last I checked and this should be plenty. There is one out there...Lucas Racing Oil I believe which has 2000ppm. At this point you may be flirting with too much and too much ZDDP will cause problems as your oil will become acidic and corrosive and you'll risk some serious damage.
