Early "Semi-Hemis"

Plymouth offered polyspherical versions of Dodge's FirePower hemi, which has the smallest bore center distance of any older Chrysler engine at 4.1875”, for 1955 and 1956 before introducing a new engine family, the A-block, mid-way through 1956.

241

The 241 (3.954 L) was Plymouth

Plymouth (automobile)

Plymouth was a marque of automobile based in the United States, produced by the Chrysler Corporation and its successor DaimlerChrysler.-Origins:...

's non-hemi version of the 241 Dodge Hemi for 1955. Bore and stroke are the same at 3.4375” (87.31 mm) by 3.25” (82.55 mm). The 1953-56 Dodge 241 and 270 polys and hemis, and also the 1955-56 Plymouth 241 and 259 poly heads, intakes, water pumps, and oil pans all interchange. The hemi and poly exhaust manifolds do not. Given a good set of Dodge 241 or 270 hemi heads, these can be bolted up quite easily to the 1955 Plymouth 259 making a Plymouth hemi with P27 engine numbers and original Plymouth intake and carburetors.

260

In the middle of 1955, Plymouth offered a bored-out, to 3.5625” (90 mm), 260 (also known as 259) (4.247 L) version. It's stroke is also 3.25” (82.55 mm)

270

The 270 (4.397 L) was Plymouth's 1956 offering. Like its predecessors, it was closely related to the Dodge 270 Hemi. Bore was 3.625” (92.08 mm) and stroke 3.25” (82.55 mm).

315

The 315 was a high-deck Dodge engine. Like its predecessors, it was closely related to the Dodge 315 Hemi. Bore was 3.625” (92 mm) and the stroke was increased to 3.80”.

325

The 325 was the largest high-deck Dodge engine. Like its predecessors, it was closely related to the Dodge 325 Hemi. Bore was 3.6875” (92 mm) and the stroke was 3.80”.