what is a 318 poly motor?
From 1957 to 1966, Dodge made the 318 polyspherical engine, or the 318a. It was modelled on the popular Hemi engine. The Poly differs in that it is a small block and its heads are polyspherical rather than hemispherical1. ... This increases power and cools the engine. The main advantage of the Poly over the Hemi is weight.