Originally Posted By: gmchevroletruck
what would be a good amount of zinc / phosphorous for a gasoline truck engine? 900 & 800 good, or just so-so?
SM oils in the -20 and -30 viscosities are limited to a range between 600-800 Phosphorous.
Pre-SM oils were 1000P max.
SG oils were 1200P. I think 1200-1400P is the sweet spot, although there are some race oils that are higher.
Phosphorous can go up to 1800 before its incremental wear protection effect stops increasing, and corrosion can start to be an issue.