Originally Posted By: 901Memphis
You can always add zinc to any grade of oil, I just don't think you need a 40 grade to maintain adequate pressure. QS defy 5w30 already has approximately 1200+ Zinc and around 1000 phosphorus. The last Rotella 15w40 VOA I saw had 1504 ppm zinc and 1350 phosphorus. Anyone who thinks 1500 ppm zinc is "barely enough" clearly doesn't understand lubrication fully.
1500 ppm zinc is what I would call maximum needed for any flat tappet high spring pressure application. Once you get too much higher than 1500 ppm, your getting corrosive.
Again, Idle oil pressure is controlled by bearing clearances and connecting rod side clearances. In hot climates, run a 20/w50 and if it is cold, run a 10/w30. Joe Gibbs or Brad Penn would be fine to, as would Rotella.
Valvoline Racing Formula has 1200ppm ZDDP, FWIW.
Again, watch valve spring open pressures - that is the #1 camshaft lobe/lifter killer. Stay under 300 lbs (275 lbs is ideal) on a street motor and you won't have any problems. ZDDP will not protect you from high open valve spring presures.