Stepped piston hitting head, options and advice needed.

Cudafever said

According to that, 62cc =9.9 But, some one need to explain "affective head volume"?
Because, that term, to me, says that i should subtract 23.5cc from the head volume. aks 72-23.5=48cc WOW not thats some compression for a open chamber head!

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In the case of KB piston specs, they mean that the 23.5 cc's is the net volume to be ADDED to the other volumes. In this case, it is the net volume of the dish and/or eyebrows below the compression height minus the volume of the quench pad above the compression height for this piston.

The number given is always net volume referenced to the compression height fer every piston Mfr I have checked; but the + or - conventions vary. For KB's, a + number is for an increase in volume and a - number is for reduced volume (like with a domed piston). Others, like JE, use the reverse convention, where a - number is for increase in total volume and a + number is for a reduction in total volume.

So you need to know the convention used by that particular mfr. The easiest way to tell is to look at a simple flat top with eyebrows for that mfr, which will always be an addition to total volume; and then just look to see if the mfr shows that as a + or a -.