DanH mentioned that #5 is his standing.
I wonder about the idea of #4 too. If more of the combustion chamber was in the piston, what would the effect be? Anybody have some thoughts on that?
Here is what I found on another forum about dish vs flat. Every time my dimly lit bulb gets a little brighter, I get a little more anxious to try it out. I have to hold back to make sure the projects are started in order, and others get finished on time. >>>
If the 'dish' is the same shape as the combustion chamber above it (so quench area isn't reduced) - then it's probably a wash. But if the 'dish' is basically slightly smaller than the full circumference of the piston, then quench area will be reduced. This can result in a less efficient burn - meaning less power, less efficiency
, less mileage, etc. Do some searching around the net - lots written on this stuff. If I had my choice - I'd have the chamber in the head and flat top below that maximizes quench area. And then be sure to have things carefully machined and assembled so the quench dimension stays nice and tight -- area between piston top and head (not inside the combustion chamber) in the .035"-.040" range.
Additionally - the head is the best equipped to remove heat from the chamber. When you flatten out the chamber (reduce chamber size) and dish the piston - you remove heat transfer area from the head, and you increase heat transfer area to the piston. Over simplifying - but likely means more thermal work the oil has to do, and less thermal work the coolant has to do. While contemporary oils are designed to both lubricate and remove heat -- you're better off if you minimize the heat transfer function of the oil and let it concentrate on lubrication.
Here's a piece I found while searching around....
"Now if you have a flat top piston with a .040 inch clearance on the squish/quench side, the effects of squish and quench are maximized by how close the piston and head deck close with each other. The effect is the same with a "D" dish piston where the dish is all under the valve pocket. However, a piston with a circular dish cannot close any more than the raised rim of the piston crown. So even if this crown is .040 inch away from the head's squish/quench deck the floor of the dish is a considerable distance away and it cannot and does not expel the mixture toward the plug with sufficient force upon compression to throughly agitate the mixture for the most effective burn. At the post ignition point, it does not provide the high surface area to volume ratio of a flat top so that the late burn's excessively high temps are not damped. Both of these conditions lead to reduced power
as on the squish phase the burn is slower and weaker requiring more timing lead which has the effect of first trying to drive the piston backwards and second increases cylinder pressure and temperature too early which combined with inadequate quench leads to detonation and preignition."
Here is a link to some other's opinions. I am not an engine builder or even have that much experience, but lots of info.
Dish piston at 10.50 WILL make more power than a flat top at 10.50???
Several years ago, I talked with a guy who built big blocks. He said the best for normal driving is a flat top. There was talk of having dished pistons because they bring the combustion chamber down into the cyl which if the circumstances are right, it improves the power because the explosion happens more at/in the piston. I personally like flat tops.
The reason a dish works better (especially at high rpms) is because it increases the VE of the engine.