Originally the ZDDP was .03 to .08% .. but oil co's realized that higher ZDDP levels were a cheap way to reduce oxidization (thickening) so they jumped the ZDDP level to .010 and beyond. But tests showed that ZDDP above .014% would eat metal.
So they reformulated the oil and ZDDP levels dropped from mid teens to low teens. Once the EPA sought to reduce ZDDP as it harms catalytic converts it went below .010%.. which was where it was originally was to being with.
If you run a super whumpa-whumpa double valve spring motor with cam profiles that look like squares then yeah, more ZDDP can help (but again, to much ZDDP will eat metal).
Any modern API oil will be fine. originally the oil was 20 or 30 weight... but a good multiviscosity oil like 5W20 may be easier to find.
Last edited by pfarber; 05/03/2015 11:54 PM.
