After a motor is broken in with break in additives and oil has been changed to a good quality oil that still has a decent amount of zddp, can you over do it on the zddp by adding a zddp additive. (Example VRI oil plus zddp additive. I know there are others too). Hope this made sense.

 

I don't think there's any reason to run extra ZDDP unless the oil you're using is SN rated. Any god oil with some ZDDP in it wont need more. I use Brad Penn 20-40 wt. in mine, and it's about $6 a qt. Regular oil at around $4.75-$5 a qt. plus $10 for a bottle of ZDDP is a bit higher in the end.

 

ZDDP is a must when you've got a flat tappet cam. We run Valvoline ZR 1 exclusively in our big block. For standard hydraulic cams the ZDDP isn't actually needed. Thank the EPA for that.