Mild 360 Magnum Build

FWIW..... In the KB world, + is actually valve relief and increases chamber volume (lower CR), and - is for a pop-up or dome, i.e., it decreases the chamber volume (higher CR). Other piston mfr's use the opposite convention. How you know is to look at a flat top that the mfr makes with eyebrows and look at their listing for whether the sign the eyebrow volume as + or -. I always go to the pistons mfr sheet as a distributor site's listing might make a mistake.

Every mfr references it relative to a perfect flat top (no reliefs) with it's flat plane defined by the compression height +rod length + 1/2 of the stroke - deck height. You can have both eyebrows AND a dome which change the CR in opposite directions, but the number shown, + or -, is the net total change from that perfect flat top model.