The Chrysler Corporation, or Mopar, manufactured many vehicles known for high performance and elevated horsepower during the 1960s and 70s, with breakthroughs and innovations that competing manufacturers later emulated. Their small and big block engines came in various cubic inch displacements, with cylinder head designs that improved through experimentation and research. Many of the special Mopar head designs have been sought by the serious high-performance car-builders and restoration enthusiasts.
The wedge cylinder heads, in concert with their engines, possessed a good combination between torque and horsepower due to their wedge-shaped combustion chambers. Produced in the mid 1950s to late 1970s, the heads were used on engines from passenger cars to motor homes. They easily fit on engines compatible with B and C body frames, making swaps convenient. They held 1.88-inch valves and over-sized exhaust ports. The last casting numbers in the Wedge heads can be identified by 286, 209 and 518 designations.
The closed chamber factory Mopar heads had casting numbers ending in 915 and 516. They came equipped with 1.60-inch exhaust valves, except for the 1967 440 hp engine with the 915 casting number, which had the larger 1.74 exhaust valves. Manufactured and equipped on pre-1968 cars and trucks, the heads had a quench-style combustion chamber that lent itself well to high-performance demands. The 1967 440 hp closed chamber head became and remained a coveted design because it was the first big block that Mopar used with 1.74-inch exhaust valves capable of producing a 13:1 compression.
The open chamber factory head design started in 1968 and lasted until 1971, displaying the 906 casting number. The head had designed features to compensate for stricter emissions and substandard fuel quality. To offset the weaker power levels, Chrysler upgraded the exhaust valves to 1.74-inches and raised the combustion height of the head to allow higher piston travel. The result gave the open chamber heads almost the same power levels and performance of the closed head design.
The Mopar hemispherical head made major improvements in torque and horsepower through its unique combustion chamber design. The 426 hemi engine debuted in 1954 as a strictly racing machine, until a domestic version came out in 1966. Mopar produced the hemi head was produced for eight years, for its earliest incarnation. The hemi head can produce a 10.25 compression ratio at over 425 hp. The heads allow for a top end 5000 rpm, with 490 foot-pounds of torque. The valve stems measured 5/16-inch, with 2 1/4-inch intake and 1 7/8-inch exhaust.
