Re: Did Chevy consider Packard V8 BB Design?

Posted by Rusty O\'Toole On 2009/3/6 2:26:35

"Rusty,

Thanks for the additional input. I think you mentioned the Polysphere being copied by Chevrolet before. What was the difference between the Polysphere and the Wedge? (And why isn't Packard's Wedge more famous than Dodge's?) BTW I noticed in the Kettering writeup on wiki that Oldsmobile wanted to advertise their 303 V8 as the "Kettering" but corporate put the kaibosh on it."

The Polysphere was more like a Hemi head than a wedge head. Chrysler brought out their first Hemi V8 for the New Yorker, Imperial and Saratoga in 1951 while keeping the flathead 6 for the Windsor. In 1954 they introduced a new V8 for the Windsor which they called a Polysphere V8.

To make the engine cheaper, they kept the basic Hemi design but modified the cylinder heads.

In a Hemi, the valves are arranged in a V shape above the cylinder. To make the Poly, they left the intake side of the head alone but moved the exhaust valve to a vertical position, putting the valves in more of a K arrangement.

This saved money in several ways. The head was narrower and lighter, saving at least 20 pounds of iron per head. The rocker arms all went on one shaft instead of 2 on the hemi. But everything else was shared with the old engine including intake manifold.

The only drawback was a more flattened out combustion chamber and a slightly smaller exhaust valve. The Poly was down on power compared to a Hemi but the difference was not noticable below about 80 MPH.

The wedge head design has all the valves in a row, at an angle to the cylinder resulting in a wedge shaped combustion chamber. This makes it easier to get a high compression ratio but restricts the size of the valves, and can also result in exhaust valve cooling problems due to the valves being crowded together with no coolant passages in between. The Kettering engine with the 2 middle exhaust valves side by side was a particular patsy for this. The Olds V8 was known for warping heads and burning exhaust valves under stock car racing stress and other high stress applications.

The big block Chev featured what they called a "canted valve" head. It has the valves at an angle and a flattened out Hemi head like a Poly.

Only Chev brought out their engine just as Chrysler was dropping the Poly head, 1965 - 66.