Ive got a lot of stuff (fancy valve cutouts on ma pistons, modded combustion chambers, etc) related to this thread actually on my car...

Basicly, as mentioned, you want as small a squish area as poss, and whatever flat raised areas on the head, should match whats on the pistons, so it all as good as touches, thats good squish, lol.

And IF you have no real choice but to have a fairly big squish (its not the end of the world in turbo engines) get rid of all the flat surfaces, edges, lumps, etc, that includes these fookin razor sharp valve cutouts n piston dishes you see, as any flat spots or sharp edges heat up and promote det, by working like a fookin diesel glow plug!

Most standard cars have a squish area on the head that match the one on the pistons, which is good, but many aftermarket or modded pistons people use, dont, so it dont match, creating a flat area with sharp edges on the head and/or pistons, just asking to get hot n promote det, like i already mentioned.

If youve not got that squish on your pistons anymore, the one on the head could well be doing more harm than good.