Was talking to one of my friends and had the completely stupid thought of, what if the pistons on an engine were square? More HP/Toruq or would it explode every time,lol.
A round shape is the statically most rigid setup for containing pressure. It makes sure the flame front reaches all parts of the cylinder symmetrically and in the shortest time possible. A round shape maximizes the volume with the shortest path into all directions radially. Sure, you could build square cylinders… but they would perform poorly in comparison, it’s not worth trying.
You also have the problem of trying to create a seal at the apex of each of the four corners. You would have to round the edges… and then you may as well go circular anyway…
On the topic of squares, I have always wondered if a car would sound different with exhaust piping made from square pipe instead of round 
I imagine you might get some weird metallic sounding resonances with soundwaves bouncing around in the corners?
Honda NR…drewl
The corners would be the hard part.
Still oval pistons work so it should be do able
Sealing the corners would be a bitch, hence oval pistons instead.
and also the pressure would try and find the weakest point, it happened to the Comet Aircraft back in the 50s with its square windows so thats why Cylinders are oval because there is no point on a circle that could get and over pressure on it…I hope that makes sense…