AMX, they have grooves to help with holding heat in. The alloy is better at being "thermally stable" and the design reflects heat of combustion. Leat that's how I understand it. Also, it slows the heat of combustion soaking into the whole piston. (we are talking the immediate combustion event, it's not like they don't get hot...) If heat can be transferred to the whole piston, it will be dissipated by the oil splashed around there. But any heat "given away" by soaking into the material is energy lost or wasted from the combustion event. That's the theory behind coating the piston tops and chambers and exh ports with thermal barrier stuff. In any event, the design does not promote detonation by it's shape, but helps stop it by the material and shape.
The down side of that alloy is the heat that is focussed on that top ring. Its room for the ring to expand that you need to "build in". The piston itself basically does not expand itself due to the alloy. Typical piston to wall is 1/2 or less compared to good forged.
Good forged also do not rattle. Diamond, CP, J&E, WISECO, and Ross are all good in terms of staying quiet. TRWs, Speed Pro, basically the older designs are not and they may be noisey when cold started. The factory cast as 71 and CP have said are a very durable design. They are very beefy, and the expansion limiters are so they can be run tight as compared to most original cast pistons from that era. The Hypereutectics regardless of manufacturer are all cast. But the alloy is much, much different in every case from the old cast stuff. Much lighter, much stronger, and much more thermally stable. I ran 175hp NOS and 320hp on factory cast pistons for yeas. It hit 7200 once or twice by mistake. But, i ended up blowing the ring lands off two pistons because I got stuck and had to run a nice old lady's 10 yr old lawn mower gas. I pinging for 4 miles basically 100 % of the time, and they broke during that drive.
Detonation will not break things by heat. It's the pressure waves created that are not always audible. If an engine detonates it is like a hammer blow from the chamber to the crank throw. Everything is hit very sharply, and that is where the brittle part of hypereutectics come into play. They are like tool steel. Tools will break before they bend. Forged pistons are elastic compared to cast. Cast are elastic compared to hypers. So when a spike from detonation hits the top of a cast piston, it tends to flex a little and can do that for a decent length of time. When it hits a forged, the piston doesnt flex much, but enough, and it's much stronger to beign with. So it's not a big deal to the piston.. It can still wreck rigns and bearings, and eventually can crack blocks and walk main caps around. But the piston can take it. On a hyper, that pressure wave hits, and the thing can deal with it for a little while without flexing because it's strong. But eventually, it simply fractures like brittle tool steel. On a running engine at say, 4000 rpm, and it detonates steady for a 10 second time frame, thats over 2500 hammer blows in 10 seconds... and that's only 4K rpm for 10 seconds.
