I am going to just add this note, After all the questions and concerns on zddp additive and oil I called the cam manufacturer I used which was Isky, they where simple, no break in oil (not even Bradd Penns break in oil) only use Bradd Penn oil period, as Roger said they told me you can't add additive as that unbalances the package the oil has. I agree if you can get a roller cam and can affordit do so, however from what Isky told me your ok with Penn oil but it must be a heavy viscosity as cam lobes are oiled by the oil fog in the valley (not directly oiled) and if a thin oil is used the oil film thickness is not suffecient to protect the lobes, they recommended 20/50. I have a sbc I have ran with solid lifters for 20 years and still runs awesome but I use the right oil, 10/40 was the thinnest oil I remember when working at a service station 30 years ago. Call Howards and see what they recommend it could be different than Isky, nobody knows more or hears more problems about this than the cam manufacturers I am sure, ask them.