Using your values, I get 9.12:1 SCR and 7.49:1 DCR. The difference in calculations could be in the head gasket volume. For the regular bore Best Gasket head gaskets, I use 10.0 cc’s.
It’s always recommended to cc the heads and ideally each combustion chamber. It’s not unusual for a variance in chamber volumes and more often than not, it will be found that chamber volumes go from small to large when examining cc values from one end to the other. In these cases, I do the math to angle cut the heads from end to end so that the chamber volumes are equalized.
I’ll also add that using a measured intake closing event at the camshaft using the recommended valve lash setting rather than what’s stated on a cam card is going to be much more accurate. Cam cards do not necessarily use the lash setting for the closing event and because the advertised duration does not state exactly what value is used, that number is in question when using it for the DCR calculation. I will get the actual intake valve closing event from the cam when degreeing in the camshaft and while getting that value, I’ll also take some other readings around it in case I want to vary the valve lash in which to alter the DCR. I trust that made sense.
Lorena, Texas (South of Waco)