the reverse domed piston (cocave) design is not to make a circle but to make the compression increase at the raised outer edges…
think cutting a sphere into 3 pieces, above the equator and below the equator.
this makes for a “cats eye” shaped compressed zone…
the curve of the piston and the curve of the head ar made to be complimentary…done right the forces can be directed almost perfectly straight down…
most flat topped pistons meet a obscurely shaped recess for the valves and plug.
it is neither based on a complimentary angle nor is it a blanced and uniform shape, so
the forces that occour at spark typically go as follows,
rpimary ignition occours causing some of the gases to burn and the rest to begin to expand from the heat and force of the immediated burn.
once the fire makes its way to these gasses they with burn and expand on their own like the rest…
but…pls remember… the correct direction for maximum efficiency is strait up or down, in line with the connecting rod and the crank…
BUT…
they will have often moved away from the plug/point of ignition, because of the initial point of ignition’s gasses moving / expanding outward…
this causes their forces to be directed like a wedding ring made of C4.
they blow out in all directions as all gasses do…BUT
some of this force is directed to the center of the ring /the other forces from the other side.
as well as down past the piston rings
as well as towards the cylinder walls
the rest of their forces are pretty much going in the correct direction.
this is why gapless rings and close tollerance pistons exist for very high HP cars…to get as much of those "misdirected forces BLOCKED so they are re-diverted to the center of the combustion zone and eventually like a lazerpointer in a house of mirrors towards the crank or head.
this is also why many high HP cars run Dual spark plugs, the spark at almot exactly the same time (depending on tuning) to get the forces directed back at the center of the combustion zone, as well as improving the “completeness” of the air/fuel mix burning and therefore not wasting any gas that could be making power…
but this is only done in cars where they are trying to get every last HP out of them…and only worth about 10-20hp in a 1200hp motor…not much by comparison, but maybe the difference between winning and losing $10,000 or $100,000 race.
the inverted dome piston takes the wedding ring of C4 model and redirects it back up, the complimenting head design forces the gas back to the center.
its only good for maybe a 10-15% increase in efficiency
but imagine a 10-15%increase in HP instead of the 10-20hp we were talking about in the 1200 hp motor!