The Polyspheric or Poly engines were V8 engines produced by Chrysler from 1955 to 1958 as lower-cost alternatives to the Hemi engines. These engines were based on the Hemi engines, using the same blocks and crankshaft parts, but completely different cylinder heads, pushrods, exhaust manifolds and pistons. They were called Polyspheric or Poly engines, because they featured polyspherical-shaped (meaning “more than one sphere”) combustion chambers. These combustion chambers were formed by the two shallow concave domes where the intake and exhaust valve seats were.