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318 (Canadian) poly and 325 (Dodge) poly

From: Hank Dozier
Remote Name:
Date: October 02, 2002


Tim... THe engines are fundamentally different. The 318 poly came out of a Canadian Fargo truck motor which was designed by Chrysler Canada. It was meant for Canadian usage and export originally, and featured a "closed" deck manifold and different bore/stroke ratio, both of which meant a different block design. It was substituted into the Plymouth line to backfill a shortage of engines caused by production capacity issues at the Chrysler engine plants in the US for Dodge engines (the 241 and 270 Dodge block). This came about because of increased popularity of V8s both in Dodge AND Plymouth vehicles in 1955. The Canadian poly, also know as the "wide" poly due to the block width since it featured a larger bore and shorter stroke, was made in displacements of 277, 301, 303, 313 (Canada only), 318 and 326 in various bores and strokes. It was never increased in deck height as were the US engines. The Dodge block, on the other hand, was made in 241, 259 (Plymouth and Fargo), 270, and with increased block deck height, 315 and 325. All of these engines had both poly head and hemi head variations, EXCEPT the 259 CID engine. Interchangeability is limited in these engines to the oil pumps (some) and timing chain/gear set only. You cannot mount 318 poly heads on a Dodge, or Dodge poly (or hemi) heads on a 318 poly. Water passages, oil feed to the rockers, oil drainback, water passages and bolt spacing is different.


Last changed: July 19, 2018