JohnF wrote:It’s all about volumetric efficiencies. Getting the best/most charge into the cylinder, then getting as much of the spent gases out of cylinder in the time allotted. Since “flathead” engines have the valves/ports located to the side of the power cylinder, it is more difficult for the gases to enter and exit combustion chamber/power cylinders efficiently. Hence the development of “overhead” and “hemispheric” valve and combustion chambers where greater efficiencies are achieved. There have been many variations of shaping the combustion and flow characteristics of internal combustion engines to maximize volumetric efficiencies. The one you see on these components is one of those.
Back in the 1970’s, Honda was able to achieve an amazing 98% volumetric efficiency @ 18,000 RPM in the racing prepared six cylinder version of their motorcycle engine. That’s a lot of gases moving in and out of power cylinders! That was a naturally aspirated engine as well. Turbochargers? That’s a complete different design theory and another topic altogether.
Thanks but my question has not quite been answered. Naturally, it's all about volumetric efficiency as it is with the performance of any internal combustion engine. So let me ask this way:
If the combustion chamber did not have that long recess above the intake valve and the chamber was just uniform smooth across its width but with the same clearance above the intake valve as it has with the recess, would the engine still perform as well as it does now if the compression ratio was still the same?
Do you think that maybe the recessed area works like a channel of sorts to better direct the air flow toward the cylinder when the intake valve opens? I can see that the ridge of the recess is higher than the valve when it opens but I'm curious if the incoming air from the valve tends to hang on the edge of the recess as the air flows toward the cylinder to fill it.