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.)
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.
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.
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."
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.)
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.
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.
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 318 | Chevrolet 283 |
---|---|---|---|
185 hp | 230 hp | 170 hp |