Vintage Engines: Mopar Polyspheres

It's encouraging for the future of street rodding that vintage engines have really come into their own lately, serving to spice up the mix and end the boredom of new crate motors in every engine bay-even in cars otherwise built to appear "period."

It does seem a little incongruous when you see a nicely done traditional rod powered by the ubiquitous just-out-of-the-box SBC. Of course they're powerful, stone reliable, and carry a factory warranty, but just when did real hot rodders start becoming as conservative as accountants or actuaries? Even dressed up with vintage-look finned goodies, these engines lack some of the reckless spirit of the 1940s, '50s, or '60s we're wistfully trying to emulate. What need is there for a no-brainer crate motor if your street rod is never going to see more than a few thousand miles a year, or worse, travel safely cocooned on or in a tr%#ler (such a dirty word).

The century we exited just eight years ago was the "century of the automobile," and the Big Three automakers built an astonishing array of engines during those decades. Some were destined for short runs, others were continually improved to stay in Detroit's accelerating technology race, but one fact remains true of just about all engines from the Model T banger onward: They were used and abused by tinkerers, hot rodders, and racers.

If you want to know why useable early Ford closed-drive rearends are hard to find, it's because the early rodders banged them into oblivion (and the Zephyr-geared '39 boxes, too) by bolting a wide variety of hotter and bigger engines into the cheap-and-light Fords that formed the basis for hot rodding and racing back then. Oldsmobiles, Buicks, Cadillacs, Chevys, Y-block Fords, and even Studebaker V-8s all served the need for speed. Hot-rodded inlines like Chevy/GMC sixes and NASCAR-winning Hudsons also proved their mettle in street/track racing. Ak Miller was snubbed by his Flathead compadres when he switched camps and stuffed a Buick OHV straight-eight into his Deuce roadster. The naysayers had to eat crow when ol' Ak pruned them all off with the 320-inch Buick, running 118 mph his first time out with it at El Mirage!

What's our point here? Just that there are a lot more engine choices out there than what you'll find in a catalog-engines that are different, and not different in the sense that you have to "dare" to use them, either. Virtually any vintage engine can be rebuilt and hopped up to be as powerful and reliable as you'll ever need in your street rod. When you combine those attributes with the "period cool factor" only a historic powerplant can provide, what's holding you back?

We're going to be examining a number of the vintage engine choices out there, specifically the "obsolete" ones that haven't been available for many years. A '57 283 Chevy may be a vintage engine, but it's far from obsolete. Parts or speed equipment for a small-block Chevy are everywhere you step. Some vintage engines, such as the Chrysler Hemi and the Flathead Ford, are so popular today, so well covered in books and magazine articles, and the subject of so much brand-new equipment that we aren't including them in this series.

We'll be looking at the history, performance, and specs of a number of engines, with tips on current sources for rebuilding and hopping them. Our first engine is the "polysphere" found in a number of '50s cars from Chrysler, Dodge, Plymouth, and DeSoto.

The Polysphere V-8S
The postwar period in automotive history found the Detroit automakers playing catch-up, trying to convert from producing war materials back to the civilian vehicles that were their stock in trade. Until 1949, the postwar cars were pretty much slight revisions of the '41 and '42 models, but once that corner was turned and production was in full swing, the engineers and designers were back trying to win in the combat of the marketplace.

While Ford went for a new chassis and very new styling, it still had the venerable Flathead for power, while GM and Chrysler forged ahead with radical new overhead-valve V-8s that started the "horsepower war" that continued throughout the 1950s and on until the "horsepower crash" of the 1970s.

The Hemi made a big splash right from its introduction in '51 Chryslers, and later in Dodge and DeSoto models. As good as their panache and performance were, the Hemi heads were expensive to produce and Chrysler sought a way to make a less-costly version of these engines to keep up production and profits after all the research money they had invested. The misunderstood polysphere engines were the answer. The Hemi owed a great deal of its potential to the half-ball shape of its combustion chamber, the even flame front with the central location of the spark plugs in the chamber, and the port routing allowed by that spark plug placement. Dual rocker shafts (one intake, one exhaust on each head) were required to operate the valves. In order to reduce the production costs, all of these aspects of the Hemi were discarded in favor of more conventional heads on the polysphere engines. The moniker polysphere refers, as does hemisphere, to the shape of the combustion chamber, with the poly chamber more like two half-ball shapes than the single half-ball of the Hemi. The poly engines used a single rocker shaft on each head and the spark plugs were "outside," between the valve covers and the exhaust manifolds. They were sometimes referred to in factory literature or manuals as the "SRS" engine, for single rocker shaft. Although they had as-cast combustion chambers compared to the fully machined chambers in the Hemi head, they were still quite efficient engines and, were they not constantly compared to the Hemi, would be remembered today as decent engines.

As it is, the polysphere engines used in Chrysler, Dodge, Plymouth, and DeSoto models are shrouded more in mystery than in performance legend. All Detroit automakers have their legions of rabid one-marque-forever followers, but the Mopar enthusiasts are in a class by themselves. No other group is so loyal to a fault; they put the fanatic in fan (and we mean that in a nice way). You have to be dedicated to deal with the million little idiosyncrasies of the Mopar brands, and the poly motors are one reason a lot of Mopar fans relate to the '60s cars more than those of the 1950s. Numerous Web discussion groups argue back and forth about the confusion of model years, part numbers, applications, and nomenclature.