Hi Guys
Oldcarmark is correct. Rotella T 15-40 still has the ZDDP in it. A few months ago I actually called Shell and (after a LOT of "let me connect you to ....") got to speak with an engineer who was very knowledgable about the ZDDP issue for flat tappet cams.
The ONLY Shell oil that still has an appropriate amount of ZDDP in it is the Shell Rotella T 15-40 which is usually considered for diesel engines. He told me that when Shell changes any formulation he hears about and works with it for about three years before it comes out on the market. He said there was no indication that this Rotella T formula was even being considered for change.
I have used it with no isues for several years although I run an additive in my 428 and Y blocks. I don't use racing oil with ZDDP (Valvevoline comes to mind), or expensive synthetics (like Amsoil) though maybe I should, break in oil with ZDDP or break in additives with ZDDP.
The most cost effective additive I've found is from Comp Cams at about $10 which I order from Summit Racing.
If you're concerned about valve seats not handling unleaded gas you can get lead additive from many auto supply stores, Walmart, or any farm type supply store. I ran the stuff in my old Ford tractors for many years.
Hope this helped
Missouri Mike
I'd rather be lucky than good.................
but good ain't bad!!