What in the world is a Poly* Head engine?

When you see a Poly Head engine for the first time you will probally ask yourself " WOW what in the world is that?"

The Poly Head engine is a logical extension of the famous Hemi* head engine of the Chrysler Corporation. Logical in the sense of cost and weight. Cost was reduced by using only one rocker shaft per head, and spark plugs were mounted ouside of the valve cover, reducing the need for spark plug tubes. Another cost saving feature was that the combustion chamber was cast and not machined like the early Hemi engine. Weight was reduced by eliminating the huge casting needed to support the second rocker arm shaft.

Below is a image of a Poly cylinder head. The area in red is the partial surface of the valve cover seat. Notice the waviness of edge. This is the external characteristic of the Poly head. No other engine valve cover has this outline.

 

Below is a 270 Cubic inch Poly head engine

 

Below are images of a cross section of the poly head, and hemi head. Notice the shape of the combustion chamber on both. Also take notice of the spark plug wire location, the rocker arm shafts, the location of the valves, and the angle between the valves.

Colored keyed Image of Poly Head and Hemi head

* Poly = Polyspherical
* Hemi = Hemispherical

For more information on th Poly head visit the Polyspherical Engine Association