1964 Pontiac SOHC V8
Most likely prompted by its development of the Pontiac OHC six, the GM division built three different experimental SOHC 421 CID V8 engines in the early 1960s. According to the engineers who worked on the project, the SOHC 421 engines produced around 625 hp and were capable of turning 7,000 rpm.
One version of the engine featured camshafts driven off the front of the engine, another design had the cams driven by gears off the back of the engine. Apparently at least one of these engines survives under the hood of an engineer’s personal Pontiac.
1967 Cadillac Eldorado V12
As part of the General Motors V-Future program, Cadillac developed an overhead cam V12 slated for production in the late 1960s. The V12 engine was to make its debut in the new FWD Eldorado in 1967.
Six prototypes engines were built in 1963 and 1964, all with a 60-degree architecture, chain driven overhead camshafts and hydraulic finger followers. The initial displacement was 7.4 L, but an 8.2 L was also tested. A number of different induction systems were tested, including a single four-barrel, dual four-barrel, and triple two-barrel carburetors, as well as mechanical fuel injection. Output ranged from 295 to 394 horsepower.
Based on the power output listed above you can see why the Cadillac V12 program was killed. Not only was horsepower disappointing, but GM was also concerned about the engine’s ability to meet upcoming mandated emissions controls.
1969 Plymouth Weslake DOHC V8
It’s unknown whether this project was purely for racing, or Plymouth had the intent to offer the motor in a street car at some point. Keep in mind that the entire Chrysler group witnessed the excitement and positive impact on the brand when the previously race-only 426 Hemi was offered in production cars.
Following the 1968 season, Richard Petty announced he was leaving Chrysler and going to Ford for the 1969 NASCAR season. The money allocated for Petty was used to develop the Plymouth Indy DOHC V8. Design work began in February 1969 and running engines were provide to Andy Granatelli’s STP race team less than 90 days later.
The designer of the special cylinder heads was Harry Weslake, a British engineer best known for his expertise in gas flow through internal combustion engines. If you recognize the name, it may either be for his V12 engine in Dan Gurney’s 1967 Belgian GP winning Eagle, or the Gurney-Weslake cylinder heads used on GT40 Fords.
The engine lacked top-end horsepower necessary to compete at the high speed oval tracks, it had plenty of bottom-end torque which made it quite competitive on the short oval. In fact, Art Pollard drove the Plymouth-Westlake engine to victory at the 200-mile Indy car race at Dover, Delaware on August 24, 1969. This would turn out to be the only victory for Plymouth in the history of Indy Car racing.
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