Posted by: Mark Polk | 2013

318 A Poly Head Engine Resources Page

318 poly head

318 poly head

The A Series 318 Poly Head Engine:

The A-series 318 Poly Head V8 engine gets its name because the combustion chambers are Polyspherical in design. The hemi designed engine was complex, expensive to build and heavy. To address these issues and concerns Chrysler designed and used a polyspherical shaped cumbustion chamber. What this did was allow the Poly head engine to use a single rocker shaft to operate the valves on either side. The rocker shaft was centered between the valves with the exhaust valve on a vertical plane and the intake valve canted toward the carburetor, like its larger hemi brother. This design positioned the spark plug in a prime location in the combustion chamber and allowed for larger valves and more efficient breathing. The Poly head engine is easily identified by its valve covers scalloped design to fit around the exhaust valve springs on the exhaust sides of the engine. The 318 A series Poly head engine was produced from 57 through 67 when it was replaced with the LA series 318 engine. The engine displaces 318 CI with a 3.91″ bore and the 3.31″ stroke.This head & engine design was coined Semi Hemi by Mopar enthusiasts.   

By adding a performance cam, 4-bbl, 2-4bbl or 3-2bbl induction, and headers to a 318 poly head engine you have a respectable small block Mopar engine powering your truck.  A rare truck deserves a rare power plant.

I wanted to include a list of 318 poly head engine resources for anybody considering using a 318 A poly head engine in their sweptline truck project.

Here goes:

  • Dual quad Carter carburetor set-up for poly engine

  • 4-bbl install on poly engine with part numbers

  • poly engine upgrades and interchangeable parts

  • Poly engine facebook page

  • Poly engine headers

  • Poly engine association;id=1;url=http%3A%2F%2Fwebspace%2Ewebring%2Ecom%2Fpeople%2Fcu%2Fum_4409%2F

  • Poly engine ID information

  • Poly engine article

  • 318 LA & 318 A engine interchangeable parts

  • 318 poly forum

  • Poly engine transmission information

  • Adding tri-power to a V8 engine information

  • Tri-power set-up forum discussion

  • Poly engine book

  • Tri-power carburetor set-ups

  • Custom camshafts

  • Decode poly engine numbers

  • Rochester 2GC carb rebuild article

  • Progressive linkage set-up information

  • Tuning progressive linkage article

  • progressive linkage set-up information

If you know of any other helpful sites for truck owners considering a 318 A poly head engine swap please let me know and I will add them to the list.

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Mark Polk

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