I made a previous post about a engine I was working on but a question popped into my head with some of the answers.

Hotspots on a engine piston

Wouldn't a piston with valve reliefs cause hotspots to begin with?

I have seen lots pistons with some deep,sharp angles in them from the factory.

 

Well yes and no, under normal operating conditions hot spots on the piston crowns are not that big a deal. Now if the engine is highly modified with an increased compression ratio and corresponding higher piston crown temps, then hot spots can be a big deal.

The valve reliefs in HHR pistons are there to allow for clearance under normal operations, the Ecotec engines have very good flow characteristics and relatively high compression ratios for production "street engines".

Plus being "Interference" engines, those reliefs allow the pistons and valves to just miss each other, until a catastrophic failure occurs. Then, as you know all too well, the valves and pistons have a "Meet 'N Greet".

 

Yes, sharp area's can get hotter than flat one's. But hot spot's are more caused by carbon buildup on top of the piston crown. The way these engines are designed there is less chance of that happening.
If you ever heard "ping" or a rattle sound in an engine, that was a pre-ignition of the fuel mixture due to (a.k.a. hot spot).
What your hearing is a shock wave going at the speed of sound bouncing off the cylinder wall as it goes back and forth across it's diameter.