1955 Dodge Coronet – That Thing Got A Hemi, Poly Or Flat Head?

During the 1950s Chrysler Corp. was unique in offering engines with no less than four distinct types of cylinder heads: hemisphere, polysphere, wedge and flathead. But the really crazy and bewildering part was that Chrysler built no less than 25 different displacement V8 engines for their 1953-1960 cars: 241, 260, 270, 276, 277, 291, 301, 301, 303, 313, 315, 318, 325, 326, 330, 331, 341, 345, 350, 354, 361, 383, 383, 392 and 413 cubic inches. (yes, there were two distinct 301s and 383s). These were all part of five unique engine families, many of which were available in either hemi or poly head versions. And there were some flathead sixes too, of course.

A lot of us gearheads knew all the engines in GM and Ford cars by heart back then but did anyone ever keep all these Chrysler V8s straight? I’m going to try to make that a bit easier here.

1955 was a very big year at Chrysler, with a complete makeover dubbed “The Forward Look”. These were the first cars styled under Virgil Exner’s term as head of styling at Chrysler, and they did what they were supposed to do: propel Chrysler out of the dowdy, short and plump era that had hurt its image, market share and profits.

The Forward Look was more than just new styling: it was also a major trendsetter towards bigger, wider and lower cars to come, especially at Chrysler in 1957. The 1955 Dodge grew a whopping 16″ from 1954, to 212″. And it gained a couple of inches in width and lost a couple in height. The ’55 Plymouth, at 204″, was also the longest in its price class.

Despite their looks, the ’57 Mopars weren’t actually any longer than the ’55-’56 cars, just lower (by 2.5″) and wider (by 3″). That really hurt their space utilization, as the ’57s still sat on a rather primitive ladder-style frame (essentially the same design as the previous years) that cut into legroom and headroom, more so than GM’s X Frame and Fords “cowbell” frame. It really helps explains why Chrysler went to unitized construction in 1960, as it lowered the floor by a couple of inches, making a significantly more commodious interior.

Although Exner was the overall styling head and responsible for the general direction and basic body shape of the ’55s, the specific styling aspects of the Dodge are credited to Maury Baldwin. But the front end does have a certain Exneresque vibe to it.

The Forward Look propelled Dodge sales forward too, up from 154k to 277k in 1955, keeping in mind that ’55 was an explosive year for car sales. That amounted to a 3.6% market share, not enough to pull it out of the #8 spot it had in 1954.

I’m not really too wild about the front end and especially the trim on the hood; the ’55 Plymouth with its hooded headlights and clean hood seems decidedly more advanced and cleaner in those regards.

Let’s not forget that completely misguided and embarrassing attempt by Dodge’s utterly mad men to create a version specifically for women. Full story here.

The Dodge (top) had a 120″ wheelbase compared to the Plymouth’s 115″. And it’s quite obvious where that was added, in the rear. At least Dodge gave the four door sedan longer rear doors so that there wasn’t that awkward filler area in those cases where this wasn’t done, like the Bonneville at Pontiac in the ’60s. The Plymouth’s wheelbase and overall proportions look more organic and better balanced; the Dodge has a Studebaker vibe to that set-back rear wheel. These endless stretching of wheelbases at the front or rear by American manufacturers were mostly design failures.

The only apparent difference in their body center sections is that the Dodge rear door opening is larger and shaped differently.

Here’s the two door sedans, just because. The Dodge is at the top. They obviously share the same side glass, front and rear. The Plymouth in both cases looks like an update on the Dodge styling, especially at the front and rear.

The exception to the rear door issue was the wagon, where Dodge (above) used the same rear doors as the Plymouth wagon, and has that dead area ahead of the wheels. Since the Dodge and Plymouth used the same wagon body shell, the Plymouth is extra long, at 208″, and the Dodge’s length of 214.9″ is all just in extra front and rear overhang.

Here’s a shot of a ’55 Dodge interior, but not from our featured car. I rather liked Chrysler dash boards of this vintage, with a fairly clean and solid look. The dash-mounted chromed shifter handle for the two-speed Powerflite automatic transmission is just to the right of the steering column.

Now we get to the tricky part, keeping all those early Chrysler V8 engines apart, especially since several of them were made in both hemi and poly (polyspherical combustion chamber) versions.

I’ve arranged them here, by their bore center spacing, from smallest (top) to largest. During the years 1956 – 1958, there were four completely distinct V8 families being built, with no basic parts interchanges and no ability to be built on the same transfer lines due to different bore centers. And during those years, three of these were made in both hemi and poly versions, for a total of seven primary variants. Yet all the hemis and polys physically looked essentially the same with similar internal architecture except for being scaled down to varying degrees from the original Chrysler hemi. Wild. Crazy, actually.

There was a bit of overlap between the divisions before the A Series engine arrived at Plymouth first, in 1956. In 1955, Plymouth, lacking its own V8, used the Dodge V8, in 241 and 259 CID sizes and only in poly (“Hy-Fire”) form. And in 1956, Plymouth still used the Dodge 270 V8, along with the new A Series 277 and 303. Also, DeSoto used the Dodge 325 poly in 1957 in addition to its 341 hemis. And of course the B came in two versions, low deck and raised deck (RB), and the 383 was made in both of those versions. And don’t even start on the differences in the Canadian versions; that gets really complicated. Got all that?

Oh, and of course the venerable old 230 cubic inch flathead six, making 123 hp, was also still available. Hemi, poly, or flat head; your choice of cylinder heads.

1955 was the first year for the polys, which were created because the hemis were expensive to build, heavy and not all that efficient. The polysphere (sort of a cross between a hemi and wedge) was created to supposedly still have some of the hemi’s advantages, be cheaper to build, and still use the hemi’s two different angles pushrods without significant changes. But then the polys weren’t so hot in any of those qualities either, as even the Chrysler engineers soon came to admit: “the performance improved by getting rid of the silly polysphere”. So next they adopted the GM solution of wedge heads for the new 1958 B series engines. The A Series poly (318) soldiered on until it too got the wedge heads (1964 for the 273; 1967 for the 318) and became the LA (“Light A”), which was lighter, cheaper, more powerful and efficient.

The top engines in the 1955 Dodge were the 270 CID Super Red Ram (hemi) V8, which was rated at 183 hp with a two barrel carb. A power pack option with four barrel carb and dual exhaust made 193 hp.  This Dodge hemi was commonly known as the “baby hemi”, the smallest of the three hemi families back then.

The poly version (“Red Ram”) had the same 270 cubic inch block. In fact, the only real difference was in the heads and manifolds, which could be swapped, if one felt so inclined. It was rated at 175 hp, with a two barrel carb. Our featured Coronet has V8 identification, and given that the Coronet was the low trim Dodge, most likely it’s this poly 270 engine under the hood.

As a frame of reference, here’s an A Series 318 poly, to show some of the more obvious external differences.

And for good measure, here’s a Chrysler 301 poly, which shows distinct features too. So now if someone says “poly” you can ask them which of the three they’re referring to.

Back to our featured car: This venerable and original Coronet has been places, as these vintage stickers attest. These used to be a big thing back in the day, and some cars had prodigious numbers of them.

So we’ve come to the end of my ’55 Dodge story. New let’s got out paper and pencil for a quiz on those engines. Starting with perhaps the trickiest one: Which engine did the 1959 Dodge Coronet use?

CC reader Jonathan F. sent me the pictures of this original ’55 Coronet, which got me going here. Note: this is a revised and updated version of an older post.