03/11/2026
Look at all those intake ports! 💪
The return of the experimental Chrysler A-925 DOHC 426 Hemi revealed one of the most fascinating forgotten engineering projects from the peak of the American horsepower wars.
In 1964, competition between American manufacturers intensified after Chrysler Corporation dominated the Daytona 500 with its powerful Hemi engines. Rival manufacturers were pushing new technology, most notably when Ford Motor Company introduced the radical Ford 427 SOHC, often called the “90-Day Wonder.” In response, Chrysler engineers began developing an even more advanced concept known internally as the A-925 DOHC Hemi prototype.
The experimental engine was based on the architecture of the legendary Chrysler 426 Hemi block, but it eliminated many traditional pushrod components. Instead, it used dual overhead camshafts mounted on each cylinder head. This design allowed the engine to use four valves per cylinder arranged in a penta-roof combustion chamber configuration, greatly improving airflow and combustion efficiency.
With this layout, the engine had a total of 32 valves—16 intake and 16 exhaust. The intake system was built to meet NASCAR rules requiring a single carburetor, but internally it used sixteen individual intake runners feeding the valves. Several components, including the intake manifold and valve covers, were made from magnesium instead of aluminum to reduce weight.
Engineers believed the lighter valvetrain and improved airflow would allow the DOHC Hemi to rev much higher than conventional pushrod engines. Estimates suggested it could exceed 7,000 rpm and produce more than 500 horsepower, an impressive figure for the early 1960s.
During testing, engineers connected the engine to a transmission driven by an electric motor to simulate high engine speeds. However, the experiment caused the tappet bosses in the block to fail, halting development before full running tests could be completed. Soon afterward, NASCAR banned exotic overhead cam engines from competition, which effectively ended the program before it could be fully developed.
Only two prototype engines are believed to have been built. For decades, the surviving complete example remained hidden in private ownership until it was finally displayed again at the Indy Mopar Trade Show after nearly twenty years out of public view. Its reappearance allowed enthusiasts to see one of the most ambitious and mysterious racing engines ever created during the golden era of American motorsports.