Combustion chamber efficiency?

[bp944]

Am I right to assume that a tall and narrow combustion chamber is less efficient than a short and wide combustion chamber? For example, A 4 inch stroke with a 3 inch piston versus 3 inch stroke with 4 inch piston. How much difference in efficiency what I actually notice? I'm looking at different ways to configure a v8 block.

[Daox]

There are plusses and minuses to over square and under square engine design. You have to strike a balance that meets your design criteria.

[NeilBlanchard]

Right, it is a matter of the RPM vs the flame spread rate -- higher RPM requires an undersquare design (shorter stroke than piston diameter), but this is limited by the flame spread over a larger area that is also very thin. A lower RPM can work well with an oversquare design (longer stroke than piston diameter) since there is a longer period of time for the flame to spread and the piston is smaller, too.

So all else being equal, I would think that an oversquare design burns the fuel more completely.

[gone-ot]

HEMI-sperical is best for power.

WEDGE with almost 'no' peripheral "squish-area" is best for emissions.

BOWL in cylinder is better for fuel economy with direct-injection (ala' diesel).

[Piwoslaw]

I once read about a diesel engine which was redesigned for even higher efficiency. One of the changes was tweeking the bore and stroke (without changing displacement) to minimize the surface area, slightly reducing the amount of heat that escapes through the cylinder walls. This might also reduce friction.