Is an SL rated automotive oil what I should be using in an old iron V8 with a flat tappet cam? After reading about the reduced level of anti wear additives in current "S" oils, I am concerned that these may not be what I should be running. Others have advised to use a 15W40 oil as this type has much higher levels of anti wear additives to promote longer cam/tappet life. I would like to stay away from 20W50 racing oil if possible, especially in colder weather. Now to complicate things even further, many of the aftermarket cam manufacturers advise against synthetic oils when running their flat tappet cams. They even recommend a straight weight 30 or 40 wt non-synthetic for camshaft break-in. After the cam is broken in they say any non-synthetic multi-vis is ok to use.