From my own personal experiences and from what I hear,if you run a hi performance flat tappet cam for sure use some GM EOS during breakin and add about 1/4 of the container during oil changes.
Synthetic oil is no guarantee of the proper additives to protect the flat tappet cam amd lifters from premature wear.Apparantly Zddp(zinc)is the best additive and many synthetic street engine oils don't contain this additive cause "modern" engines have been designed around the lack of zinc.
Valvoline makes several grades of synthetic and conventional dedicated racing oils with enough zinc.They are labelled as racing only,this is probably to limit claims against using then in engines with catlytic convertors that can be fouled by the zinc.
Most oil manufacters have websites where you can check out the oil and judge for yourself.
