Allright---------when doing lots of engine stuff at races, etc and you want to change cams, or just the timing of them----in the cylinder that is 180 opsitite of #1---( in chev/mopar firing order it will be #6)you put two pieces of round stock that is lifter diameter and exactly same length into the 2 tappet bosses--with a straight edge across the tops you can determine when the cam lobes are exactly same rise and that will equal exact split valve timing centerline------at that point set the crank back from tdc to advance cam timing and forward from tdc to retard cam timing----it is helpful to have a cam drive like a Jessel belt or Donovan etc gear drive to make easy the adjustments


over the years of racing--I've had several cams ground that had the exact same base circle so I could quickly change cams without having to adjust the valve gap clearance