Stockish 340 upgrades, cam needed

The 7.5 cc volume in those pistons is not just the valve reliefs, but the bevel on the outside of the piston. When you remove the bevel, you can actually get a compression increase depending on how far the piston is out of the hole (like my buddy’s 340 with a .023 positive deck and a similar piston). So aside from milling the top, enlarging the valve relief to a common trough is an effective addition to lowering compression.