Here’s the latest reader question, along with my reply!
BD asks: Yesterday I had an interesting thought. What if the engine’s cylinders were square instead of circular? Yes, I understand they would cease to be “cylinders,” but it’s about what they would gain. The cross section of an engine block is rectangular, so square cylinders could accommodate more area, and thus, more volume for a given cylinder length. The area of a circle is (pi)r^2, and that of a square is 4r^2, the ratio is 4/pi, which is ~1.273, so a square “cylinder” would gain you 27.3% more volume! That means a 350 small block Chevy could be increased to ~446 cubic inches without changing the size of the block. My question is, have you ever heard of this? Has any engine been built this way? I reckon the primary difficulty would be “boring” the cylinders, but construction shouldn’t be impossible.
My reply: I’m buzzing along on too much coffee and not enough sleep but, if I recall, this has been tried and for the reasons you lay out – but the main problem is effectively sealing the right angles (i.e., the “rings”) of a square. With a circular piston the rings can expand and contract to uniformly bridge the gap between the piston’s surface and the cylinder wall, necessary for both compression and oil control. A related problem could be differing thermal expansion of a square vs. a cylinder and flame propagation characteristics one vs. the other.
Machining is another issue. Here’s a good video:
It’d be fun to cast some and see, though!
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