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It is similar in concept to the hemi engine, both in design and purpose, but a hemispherical cylinder head is limited to only two valves without the use of a more complex sub-rocker assembly. The four-valve penta engine design was invented by Peugeot of France, [ citation needed ] to be first used in the 1911 Indianapolis 500 race.
Cylinder head porting refers to the process of modifying the intake and exhaust ports of an internal combustion engine to improve their air flow. Cylinder heads , as manufactured, are usually suboptimal for racing applications due to being designed for maximum durability.
Absolute cylinder pressure is used to calculate the dynamic compression ratio, using the following formula: = where is a polytropic value for the ratio of specific heats for the combustion gases at the temperatures present (this compensates for the temperature rise caused by compression, as well as heat lost to the cylinder)
A crossflow head gives better performance than a Reverse-flow cylinder head (though not as good as a uniflow), but the popular explanation put forward for this — that the gases do not have to change direction and hence are moved into and out of the cylinder more efficiently — is a simplification since there is no continuous flow because of valve opening and closing.
The main advantage of the reverse-flow cylinder head is that both the entering inlet charge and the exiting exhaust gas cause a tendency to swirl in the same direction in the combustion chamber. [1] In a crossflow head the inlet and exhaust gases promote swirl in opposite directions so that during overlap the swirl changes directions.
This is also common for motorcycles, and such head/cylinder components are referred to as barrels. Some engines, particularly medium- and large-capacity diesel engines built for industrial, marine, power generation, and heavy traction purposes (large trucks, locomotives, heavy equipment, etc.) have individual cylinder heads for each cylinder ...
A hemispherical head ("hemi-head") gives an efficient combustion chamber with minimal heat loss to the head, and allows for two large valves.However, a hemi-head usually allows no more than two valves per cylinder due to the difficulty in arranging the valve gear for four valves at diverging angles, and these large valves are necessarily heavier than those in a multi-valve engine of similar ...
Crossflow cylinder heads are used by most modern 4-stroke engines, whereby the intake ports are located on one side of the combustion chamber and the exhaust ports are on the other side. The momentum of the gases assists in scavenging during the 'overlap' phase (when the intake and exhaust valves are simultaneously open).