240 thou. (give or take a few) so that equates to just over 6mm in the new speak.

Thats not a big favour at all. I'll grab my verniers and have a measure up tommorrow. (If I remember. lol)

With the massive dish of these pistons, I'll likely wind up with a very low CR as you've pointed out. Hence I'll have to run insane boost.

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

having just got mine back from the machine shop
my first thought was that the head you put pics up of had smaller chambers than the a series,

So with 10x the dish and a H75 open style head you should be able to stuff a fair bit of fuel in there ;)

edit - once you go turbo that is -

The E15 chamber is just over half the CC's of the A series ones. So it'd stand to reason that the CR would be very low indeed.........

So Long as you hav the right Comp ratio all the same rules aply as an N/A motor. flow, swirl etc.. So maybe find out what CC's you need for your desired comp ratio and use the head (that perhaps after a little work) will hav the right capasity.

I'd like your thoughts on which cylinder head is going to work best in this situation.
In the future, I'm going to build a turbo A14. I was lucky enough to pick up these

For a good price. They're unused, and have ceramic coated crowns and teflon coated skirts. E15eT pistons have the same comp height as the A14, but they have 10x the dish volume. This will enable me to run zero deck for good squish, but still have a nice low CR.
now the combustion chambers from this engine look like this

[img width=300]http://kachi-snimka.info/viewer.php?id=cqs1252427541x.JPG[/img]



So considering people strive for nice small chambers on HiPo N/A motors to get good compression, what chamber configuration do you think would work best with these pistons?
I have a GX head, and H75 (40thou shaved) and numerous H89's. Considering the large surface area of the dish, would I be better to use a chamber that is open to mirror the piston?