The subject has been discussed numerous times but a recent Hot Rod Magazine article has prompted me to bring it up.  A switch from conventional to synthetic oil picked up 15 horsepower on the dyno. A local reputable engine builder confirms this. According to a previous post Ted does not recommend synthetic. It’s my understanding that Mobile recommends 10w40 High Mileage for flat tappet cams. I used Valvolene VR1 for break in and after break in with no problems. Picking up 15 horsepower by switching oil appeals to me but not at the risk of destroying a cam.  Opinions please and actual experience please.  I ran Mobile one in a previous build of the same engine for a while with no problems but I’m overly cautious about damaging the build. It runs too good to mess it up.