Originally Posted by Mad-Max


But, ZDDP is the kicker - if you've got a flat-tappet cam you for sure need the high-zinc oils


In general, no you don't NEED high zinc oil.

It depends on the application, mostly the cam and valve springs.

Something like my 51 Plymouth's stock flathead does not need it, never did and never will. A stock 318/225 nope.

Something with a high/aggressive lift cam and the appropriate springs, yep.