hemispherical shaped combustion chambers.
as opposed to a wedge or pentroof (triangular with a flat spot where the spark plug sticks out).
chrysler designed it in the 60s and blew everyone away on the race tracks with the superbee.
it was grossly in-effecient back then and usually resulted in raw fuel leaking out of the tail pipe.
now adays, almost all engines are hemispherical ("hemis", except the term is patented by chrysler so none of the other guys can call them that) with a centrally located spark plug and a "swirl valve" that releases a last minute burst of combustion gasses to ensure 100% (or as close as possible in real world conditions) burn rates.
if you are getting bad gas mileage, its not because its a hemi but because its a big stupid vehicle that you bought because you felt cool sitting behind the wheel.
my car is a hemi and i get upwards of 27mpg with me beating the snot out of it like im on an F1 track.
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Jesus? No, but there is indeed a god shaped hole in the heart of man, why is yours so empty? -- snarf igraine
the original monotheism:
http://en.wikipedia.org/wiki/Phallus
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