331 Polyspherical Engine..whats the deal?

[xxwelderxx]

So I came across this type of engine in a book. They really didnt explain too much about the engine. Is it a good engine? Will it fit in my 53 Plymouth Belvedere? It seems like its the cheap verson of the Hemi.

What would be the desired set up for an engine liek this?(tranny, rear end, etc etc)

[hotroddaddy]

I had one in my fury,i was told it was a 318 though, from what my expert mopar buddy told me when i had it, is its not much of an engine, really hard to keep the valves adjusted, and not much for upgrades, he told me to scrap it for a 440, but thats just his opinion

[R Pope]

The 331 Poly is, as you said, the economy version of the Hemi. The block is the same, except for some minor machining in the pushrod holes. The heads are simplified for cheaper manufacture, with only a single rocker shaft instead of the Hemi's two. The intake is the same as the Hemi, the exhaust more like a conventional OHV engine. The 318 is a different case, there never was a Hemi version of it.
Find a set of 331 Hemi heads, they'll fit your engine. Your manifolds work, you need the Hemi exhaust pushrods though, different length.
As for it fitting your Pilgrim, well, that depends on what your definition of "fitting" is. It'll go in there, but it ain't easy.The steering box is in the way of any V8, as I recall.

[Mike P]

Pope is right, but not quite as simple as it sounds.

The intake and exhaust are different. The intake usually has a mismatch on the heat crossover. THere were alos cooling systems vevisions over the years so certain heads/head gaskets will not interchange.

THe big one is the pistons, the valve reliefs are located differently and poly/hemi pistons must be used with the appropriate heads.

The conversion is reasonably simple, but it does require careful selection of parts.

The Poly heasds were a pretty effecient design and although not as visually impressive as the hemi's they are a good engine in their own right.

[R Pope]

The 331 might be different, the 354's were interchangeable. Did it a few times, back in the day.