Concave verses flat top on piston

[Alan Elzer]

Is there any advantage between the two or does it matter on engine size, if so why

 

[Andrea Kalina]

Is this regarding cylinder head shape? That is, the cylinder head surface bounding the combustion chamber?

 

[Alan Elzer]

Is this regarding cylinder head shape? That is, the cylinder head surface bounding the combustion chamber?

Thnx. But wanting to know advantage or disadvantage of to 2

 

[Andrea Kalina]

Assuming the entire piston top is characterized by a continuous concave surface (that is, there's no flat-top annulus surrounding the concave surface), a concave piston will decrease combustion chamber surface area, assuming you're running the same compression ratio as with a flat top piston. Reduced combustion chamber surface area (especially during the early stages of the combustion event) reduces heat transfer from the combustion gases to the chamber walls, resulting in greater engine efficiency and more power. That's a benefit. As for a disadvantage, when it comes to engineering pistons like this, it can be more challenging to keep the circumference of the piston top sufficiently cool, and this can lead to durability issues. Fun stuff.