Polyspherical Head V8 Engines: 277, 301, 331, and 354
Bill Watson wrote:
The poly head first appeared in 1955, with Plymouth using Dodge's 241-cid (3.44" / 3.25") block with different heads. Dodge, meanwhile, bored its engine from 3.44" to 3.63" for 270 cid. In mid-year Plymouth bored the 241 to 3.56" for 260 cid. Plymouth used the 270 with poly heads in 1956, but replaced it with a new 277 engine, the first A block. It shared little with the Dodge V8 and came only as a poly. The early hemi heads will not fit on the A block. In 1957, the 301 produced 215 gross horsepower at 4,400 rpm and 285 lb-ft of torque at 2,800 rpm, with compression of 125-165 psi. Taxable horsepower was 49 hp. The similar 277 cubic inch engine in that year produced 197 hp @ 4,400 rpm, 270 lb-ft @ 2,400 rpm.
Engineer Pete Hagenbuch wrote:
I don't know who invented the word "polyspherical" but the design was supposed to maintain the characteristics of the true hemi with one rocker shaft and attendant cost savings. What it wasn't was a wedge chamber with inline valve stems.
The first Chrysler production hemi was the 1951 "Double Rocker" 331 cid "Firepower 180" V-8 built at the Chrysler Jefferson plant. The next was the 1952 Desoto 276 cid and built at the Desoto plant, more recently known as the McGraw Glass Plant. Next was the Dodge 241 cid in 1954 built at Dodge Main, now the scene of the large GM "Poletown" assembly plant.
The Chrysler Jefferson plant, DeSoto plant (more recently known as the McGraw Glass Plant), and Dodge Main (now the site of a large GM plant) each had their own poly and when the A engine, built at the brand new Mound Road Engine Plant, came out, it was a poly also, of 277 cid. What Chrysler was learning was the old Yankee creed; "There ain't no substitute for cubic inches", and at a time of ridiculously low gas prices, nobody cared.
Just one detail before I go on: prior to the 1956 model year, which means 1955 models only, Dodge was the source of Plymouth V-8 engines, a 270 cid poly. The next few years it gets a bit blurry. Dodge's hemi got to 315 cid, Desoto's to 341 cid, and as I'm sure you know, Chrysler had 354 cid in 1956 and 392 in 57 and 58 (Imperial and 300D only in 58). In 1958 the B Engine arrived in two sizes; a 350 cid for the Plymouth Fury (still a special model - it became the whole show in 1959) and 361 cid for Desoto and big Dodges. Other Dodges got a 325 cid A engine from Mound Road.
The LA (for Light A) engine was developed with, you guessed it, a wedge chamber, first as a 273 cid and then as a 318. Remember, this was the time the car lines expanded to three bodies, A, B and C. The 273 was limited to the A and B bodies with the 318 or B Engine in the C Body, which was new to Plymouth at the time, and named, what else?, Fury. We establish a hallowed name with some meaning to it, and then we bring it down like a statue of Saddam Hussein!
Later came the 340 and then the 360, both with wedge chambers. And now, the one time state-of-the-art Mound Road Engine Plant is empty. And the brand that used the majority of its production has disappeared too, to join ranks with names like Packard, Hudson, Desoto, Studebaker, Nash and Willys. Next to join this group will be Oldsmobile, another of the pioneer nameplates to be tossed aside. It seems that a cherished name with a long history is not considered of value in this day and age. Too bad.
About the poly engines
Christopher Cortel noted that the poly head engine is a logical extension of the famous early Hemi-head engine, reducing both cost and weight. By switching to a single rocker shaft per head and mounting spark plugs on the outside of the valve cover, an expensive rocker shaft, bracing for the second rocker arm shaft, and spark plug tubes could be eliminated, saving a good deal of money and weight. The combustion chamber was cast, not machined as Hemi engines were. The pistons and rods were also different.
From the outside, the poly can be easily identified by a wavy-edge valve cover.
As an example of the difference in efficiency, the 1958 354 engine was available in both forms. The Hemi produced 350 horsepower, and the Poly a healthy 310 horsepower. But the Poly is much cheaper and lighter.
Another example, noted by Bill Crews, is the Dodge 270 - a hemi design in 1955, and a less-expensive poly in 1956.
The polyspherical heads were ahead of their time, as were the hemis. The "Spitfire" heads had canted valves in a cross-flow arrangement, gaining much of the advantage of the hemis, but much less expensive to make. This design would make a comeback in the 4.7 liter V8.
The poly head engines were made under a variety of different names, including Fire Dome (DeSoto) and Fire Power (Chrysler). Hemi Central has information on the hemi-head versions, while Canadian engines has details on Canadian-built engines. Additional specific engines can be found here.
We have pages on poly engines sold under the Red Ram and Super Red Ram labels - click here.
