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Mopar A Engines

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Mopar A Engines

Essential contributors to this page include Shannon Mafodda, Bill Watson, Joshua Skinner, Carl Payne, Dan Stern, Steven Havens, Jim Forbes, Peter Duncan, and Hemi Andersen.

by David Zatz

Chrysler's very first V8 engines were the famed Hemis, or, as they were known then, "double rockers." A cheaper version of that engine series, modified for faster production and lower cost, was made from 1956 through 1967 in the United States and Canada. (Original plans also called for a V6 Hemi for Plymouth.)

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Chrysler had already made simpler versions of their "dual rocker" Hemis by switching to polyspherical heads with a single rocker arm shaft for each cylinder head (rather than two in the Hemi), no spark plug tubes, and a cast (not machined) combustion chamber. Dodge could then supply Plymouth with some V8 engines, but not nearly enough to fill demand.

According to Willem Weertman in his book Chrysler Engines, the new engines were designed to be compatible with the Mound Road plant's automated equipment; to be lighter; and to be simpler, so they could be cheaper and faster to build. To provide room for future growth, the engineers expanded the bore centerline spacing to 4.46 inches and the deck height to 9.6 inches.

Auto part Engine Automotive engine part Motor vehicle Carburetor


The term "A engines," according to Weertman, came about when engineers lumped together the US and Canadian versions, using the program designator. That would lead to calling groups of engines B, RB, and LA in later years.

The A-engines had polyspherical heads, like the "semi-hemis;" one major difference is in the way the "valley" is covered. The older engines had a separate valley cover; to save time and money, the A-engines used the intake manifold to cover the valley, instead. Both series of polyspherical-head engines looked rather similar otherwise, with their scalloped valve covers and rear-mounted distributors, but looks can be deceiving.

For one thing, the rocker pedestals were integrated into the head casting, rather than being separate, to cut costs and production time. To save weight, they used die-cast aluminum for the timing chain cover and (eventually) the water pump body, while prior Chrysler V8s had used cast iron. 16 oil feed holes were drilled into the semi-Hemis; the A engine replaced those with two oil galleries, drilled through the length of the block and reaching the tappet bores. They also eliminated the oil filter adapter by attaching the filter directly to the side of the block. Finally, they used solid mechanical tappets, adjusted by screws in the rocker arms.

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The 1956 Plymouths had the first A-block engines, displacing 276 cubic inches (the company advertised it as 277 cubic inches, which is how we will refer to it from now on), close to the 270 cubic inch Dodge engine. The Canadian plant in Windsor, Ontario, later that year, built a 303 cubic inch version, with a larger bore; both were made with a choice of two and four barrel carburetors.

The American engine was rated, at launch, at 187 hp with 265 pound-feet of torque with the two-barrel, and 200 horsepower with 272 pound-feet of torque with the four-barrel. Confusingly, it was given the same name ("Hy-Fire") as the Dodge engine used the prior year; the four-barrel version was "Hy-Fire with Power Pack."

1960 Ford 292 Dodge 318Chevrolet 283
185 hp230 hp170 hp
292 lb-ft 340 lb-ft 275 lb-ft

The Canadian 303 engine was installed into the 1956 Plymouth Fury, then a specialty muscle car; as equipped, it was rated at 240 horsepower. So equipped, the car broke records for the flying mile (124 mph) and standing start mile (82.5 mph). The same car, with a 300B intake and dual carburetors, hit 148 mph in the flying mile. It seemed that the less expensive block was quite capable.

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For the 1957 cars, the 277 (276) continued with a two-barrel carburetor, now rated at 197 horsepower; but it was joined by a 301 cubic inch version, essentially the same engine but with a 3.91 inch bore. There were two and four barrel versions, again, with 215 and 235 hp ratings.

The Plymouth Fury had a special, Canadian-built engine, with a larger bore and stroke than the 277 (and the same bore as the 301): the 318. With dual four barrel carburetors, it was rated at 290 horsepower and 325 pound-feet of torque, quite an improvement over the impressive 1956 Fury engine. A two-barrel version of the 318 was rated at 230 horsepower, and the standard four-barrel was rated at 260, where they would stay through the 1962 model year.

1957 277301318 (Fury)
Gross Horsepower [email protected],400[email protected],400230
Torque (lb-ft) [email protected],400[email protected],800340
Compression 125-165 psi
Bore x Stroke 3.75 x 3.125 3.9 x 3.125 3.9 x 3 5/16
Compression 8:18.5:19.25:1

The 1958 cars debuted the "B" engines, which could go up to much larger displacements than the "A" series, replacing the remaining Hemis. They used a "wedge" combusion chamber, lighter and cheaper than the polyspherical setup, but producing more power because it had more "squish" area, allowing higher compression without detonation or pre-ignition.

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For the 1958 cars, the only Mound Road engine was the 318, rated at 225 hp and 330 pound-feet with a two-barrel carburetor, or 250 hp and 340 pound-feet with the four-barrel. The Fury, with two carburetors, stayed at 290 hp, boosting torque to 330 pound-feet. Hemi Andersen wrote about the reason for this:

The reason why they standardized on the 318, and on specific sizes for the "B" engines, was because the 1955 through 1958 V8 engine and parts mix was so complicated, even the parts books had a hard time keeping up with different versions of the same type engines. I tried to find the timing cover for a 1956-58 A engine, and it all depended on car model and VIN; I couldn't find a part number I could rely on.
Windsor, meanwhile, used a new bore size with the old stroke to create a 313 cubic inch version, which would be their sole V8 through the 1964 model year.

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Dodge wrapped up their unique V8s in 1958, and joined Plymouth in using A-engines in their 1959 lineup. They asked plant engineers to create a new engine that was larger than their old 325; and thus was born the unique 326 cubic inch A-series V8 - the only A engine with hydraulic valve lifters - by using a larger bore than the 318. It was rated at 255 hp and 350 pound-feet with a two-barrel carburetor. This engine was dropped after just one model year; 1960 Dodge buyers found a 318 under the hood, unless they had ordered something stronger from the B-engine line (which had been optional since the 1958 model year). Both the Dodge 326 and the standard 318, when fitted to Dodge cars, carried the Red Ram name, as the "semi-Hemi" had.

1962-66 318 Truck2-barrel4-barrel
Gross Horsepower 200 or 202230 @ 4,400[email protected],400
Torque (lb-ft) 286 or 288340 @ 2,400

Truck engines were modified for greater longevity, with special valve coatings and rotators, more durable materials, and other materials and design changes.

Nicholas Challacombe pointed out that the Bristol 407 came with the 313 (5130 cc) and a four barrel Carter carburetor, producing 250 horsepower. All but the last 18 Bristol 408s came with the same engine; those few came with the 318.

The last A engine in the United States was made in 1966, but it continued one more year in Canada. (Hemi Andersen pointed out that Canadian-built, US-sold large cars such as the 1967 Plymouth Fury and Dodge Polara would still use the A engine.)

Auto part Engine Automotive engine part Carburetor Automotive super charger part

The Dodge truck engine above likely had Stellite seats and sodium-filled exhaust valves; all valves would have rotators built into the valve retainers, for longer life.

The US-built 1967 LA 318 has
engine number prefix C318, while the Canadian 1967 poly A 318 has engine
prefix CC318. (The first "C" stands for the 1967 model year; the second
"C" in the poly engine stands for Canada.)

The A-engines were replaced by the lighter LA series, which weighed 55 pounds less, partly due to a lightweight casting process but also because the LA engines switched to wedge heads. Willem Weertman, the legendary engine designer, said,

http://mopars.50megs.comI was in charge of design for the LA engine conversion. The biggest difference between the LA and A engines is really the valve arrangement. We went from a skew valve type of arrangement on the A-engine, which had the exhaust valve parallel to the bore, and the intake valve tipped toward the intake manifold giving what has been described as a polyspherical chamber.

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When it came to the LA engine we made all the valves tipped to the intake manifold and inline (as viewed from the front of the engine), giving it a wedge shaped combustion chamber. The reason we went to such a change, which triggered totally new cylinder heads and manifolds for the engine, was that ... the older A engine was simply far too wide at the cylinder heads in order to go into the [new compact] car.

... [we] wanted to have engines much lighter than what a conventional A engine would be. ... That triggered a new casting process for the cylinder block that allowed us to make all the walls thinner and we took a lot of the weight out of the block.
Hemi Andersen pointed out, though, that just as the A engines were based closely on the original Hemi V8s, the LA block was fairly similar in design to the A.

I've had an A engine and a late LA 318 upside down; except for the core plugs and the engine mount tabs, they are virtually identical. The "A" engine is just another step away from the original Hemi, in the big scheme of things. The first A engine, the 1956 277, was a heavily modified 270 Poly, but it was still closely related to the original 331 Hemi. They got the next engine series, the LA, all the way to 340 cid before they had to change the block to create the 360.
Canadian notes (Bill Watson)

The 303 was powered the Canadian 1956 Dodge Custom
Royal (2-barrel) and 1956 Chrysler Windsor (4-barrel). In 1957, it was the standard V8 in the 118" wheelbase Plymouth and Dodge cars.

The 313 V8 appeared in 1957 in the Canadian Custom Royal. For 1958,
the 313 became the standard V8 for the 118" wheelbase Plymouth and
Dodge models. It was available in Plymouth and Dodge models through
1964, and was replaced by the 318 for 1965. The poly 318 was last used
in Canadian production on the 1967 models.

The Canadian 1958 Dodge Custom Royal used the poly version of the
354, shared with the Canadian-built DeSoto Firedome and Chrysler
Windsor. Chrysler of Canada did not start using the B block V8 until
1959.

Also see

EngineYearsBoreStroke
27719563.753.12
303 1956-573.813.31
3131957-643.883.31
3181957-673.913.31
326 1959 (Dodge)3.953.31

All the A engines had 1.84" intake valves and 1.56" exhaust valves; five main bearings; and a chain camshaft drive, with the oil pump and distributor at the rear of the block. Firing order was always 1-8-4-3-6-5-7-2.

(Repair tips | Performance tips)

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