In a perfect world, where we have massive cash, and manufacturing plants at our beck and call, turbo or not, the way to avoid detonation, and get maximum burn quality is to squeeze the mixture into a tight ball. more or less a globe shape, or as close as we can get. A pancake, is long and flat and not too tall, and the flame takes a lot longer to spread, requiring more ignition advance and doing more negative work.

You also need to make sure there aren't remote enough sections of the charge that the flame gets there so late, it's been compressed so highly by the rest of the burning charge that it detonates instead of deflagrates (which is a controlled steady burn - incidentally - firearms require deflagration too, detonation will blow guns apart, and can happen with insufficiently packed bullet casings where a small amount of the gunpowder resists initial burning and undergoes a secondary detonation).

Obviously we are somewhat at the mercy of the combustion chamber shape. So the 'go' would be to utilise a closed chamber head, and run custom machined pistons that are flat where there is the flat head deck surface, and have a deepish dish that is a mirror image of the combustion chamber. Basically it gets you maximum quench (for any give compression ratio) and the tightest most sphere shaped charge packing at TDC.

For any given compression ratio and fuel octane, that design would allow the most boost without detonation, and even at lower boost levels, it would make more power than an more open chambered head with the same comp ratio and boost (some of which would be purely down to the sort of ignition advance each would have to run, but some of which would also be down to plain old efficiency).

What you'd basically end up having to do, most likely, is to get custom forged pistons with very thick decks, and have them custom milled to suit the combustion chamber shape.

That's the perfect world. If you are on a budget, the basic 'deal' is simple - just run a lower compression ratio than you would otherwise have to, to 'play it safe' . So if this 'perfect' piston/head combo allowed 8.5:1 and 15psi on pump fuel, then you'd look at 7.5:1. The overall power output would still be well high enough. Boost makes power - lots of it, and even the worst turbo setup imaginable would be able to outgun a very big dollar NA race engine. And last longer (due to lower rpms)

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Now specifically on your head - it looks as if there will be little quench with the e15t pistons, so the chamber shape as such isn't important. I'd probably look at the closed chamber gx head if I could get one, since it'd have the most flow potential and also bring the comp up a little (it'd probably still be well below 7.5:1 but I'm guesstimating..)

Could I ask a big favour - could you take another pic of the piston with a steel ruler going down the side of it - the distance from the crown to the top ring land looks like it's almost enough that they could be machined down enough to fit into an a15