The real 427 Mystery Motor, unlike the Z11, was not available in a car or to the public. You had to have serious NASCAR cred to get one of the 20 built.

MARK II - CHEVY’S MYSTERIOUS 427!MARK II - CHEVY’S MYSTERIOUS 427!In the 1960s, Semon “Bunkie” Knudsen always seemed to be one step ahead of GM Chairman Fred Donner’s missives disallowing factory involvement in racing. While running Pontiac, Knudsen had supported the Super-Duty Group that, after he left, managed to get 421 Catalina Lightweights to drag racers before the axe fell. In 1961 he moved on to Chevrolet and supported the RPO Z11 drag racing and clandestine NASCAR 427 Mystery Motor projects. Both pure racing programs survived, even though GM was officially out of racing. In the case of the Mystery Motor, everything was conducted through Chevrolet’s backdoor.

The surviving 427 Mystery Motor had been on display at the engine plant for many years and is currently in Detroit. Ken Kayser, above, right, is pictured with the survivor engine. He had been Business Case Manager for Mark IV engines at the Tonawanda, NY engine plant when the Chevy big-block was king of the road.

Except for cooperating with Ray Brock for a story in the May 1963 issue of HOT ROD, Chevrolet PR did not distribute any photos or information, or discuss the Mark II 427 with media. As far as Chevrolet was concerned, the engine did not exist. The Mystery Motor rattled the troops at Daytona, generated reams of misinformation and became a cult engine.

The 427 Mystery Motor makes use of the same bore/stroke block – 4.31-inch bore and 3.65-inch stroke – as the Z11. But that’s where the similarity ends. Unlike W-Series engines with combustion chambers in the cylinders, the Mark II utilized canted and staggered-valve (Porcupine) heads with conventional chambers. This style head debuted in production 396-427 Mark IV big-block engines, affectionately dubbed “Rat Motors” by enthusiasts.

MARK II - CHEVY’S MYSTERIOUS 427!Although developed primarily as a NASCAR engine, Chevrolet did produce a singular variant for street applications. Most likely the Mark II in street trim, displayed for many years at GM’s Tonawanda, NY engine plant, was built to justify the expenses of building a racing-only engine. It is possible that at some point the project was referenced internally as RPO Z33. That would have been done only to disguise the 427 as an optional production engine so as not to attract unwanted attention. Interestingly, the Mark II engine was not produced at Tonawanda, the facility best known for Mark IV 396-427-454 engines.

One of the industry’s top engineers, Richard “Dick” Keinath, had the lead in designing and developing the Mark II engine. The program started in 1960, before Bunkie Knudsen arrived and wrapped up in November 1962. To keep it off the radar, development of the Mark II and its testing by pro drivers in NASCAR racecars, was conducted at GM’s Winter Proving Ground in Mesa, AZ rather than in Milford, MI.

Part of the mystery surrounding the Mark II engine can be attributed to its planned public debut on February 24, 1963 at the Daytona 500. The first couple of engines were shipped to Smokey Yunick for use in Chevys being prepared for the 500. Junior Johnson and Johnny Rutherford were two high-profile racers originally slated to run this engine.

However, Mark II 427s were in two Z06 Corvettes competing in the 250-mile American Challenge Cup at Daytona on February 16! This was a race for sports cars and one-offs, not NASCAR stockers. Few people at the time realized that two of the split-window Sting Rays in the Challenge Cup had Mark II Mystery Motors under their hoods. They were actually the first big-block Corvettes.

To better understand how this happened, you only have to look at some of the major players involved in Chevrolet and Corvette racing: Zora Arkus-Duntov, Vince Piggins, Mickey Thompson, Smokey Yunick and, of course, Chevrolet boss Bunkie Knudsen. Bunkie was extremely close with Thompson since his days at Pontiac, and he helped Mickey set up Thompson Enterprises to front for Chevy racing activities. He also had a long-standing relationship with Smokey and his, Best Damn Garage In Florida.

MARK II - CHEVY’S MYSTERIOUS 427!Smokey prepared two Corvettes like NASCAR Grand National stockers and installed Mark II engines with HD three-speed transmissions. Small, unobtrusive Mickey Thompson hood scoops were installed in the center of the Sting Rays’ hoods for intake and magneto clearance. Scheduled drivers were Junior Johnson and Rex White. During practice, Junior was not comfortable with how his Corvette was handling at 160 mph and decided not to drive. Bill Krause replaced him and went on to finish Third. He beat other Corvettes, Ferrari GTOs and Porsche Carrera Abarth GTLs. Driving a Pontiac Super-Duty 421 Tempest, Paul Goldsmith won the three-hour race, followed by A.J. Foyt driving a Nickey Corvette! Bunkie was not unhappy! Unfortunately, Chevrolet was more of a disrupter than a winner at the Daytona 500. The Mark II 427 was less-than-legal for NASCAR since it was not a true production engine. Chevrolet had a huge fan base – and Bill France simply looked the other way.

MARK II - CHEVY’S MYSTERIOUS 427!Johnny Rutherford drove Smokey’s #13 car and finished 9th, the best finish for a Mystery-motored Chevy. Rutherford lapped the track at 165.14 mph, setting a closed course record. A broken distributor in the #3 Ray Fox/Holly Farms Impala sidelined Junior. He did win 7 of the 55 Grand National races in 1963, including the Charlotte 400. With no factory support for the engine, the car was parked. It ran its last “race” on the five-mile Goodyear Tire test track in Texas. Goodyear used it for baseline testing when finalizing tire development for the 1964 Mopar NASCAR Hemi stockers.

While no longer a mystery, there remains a variety of opinions as to quantity built and power output of the Mark II 427. According to a 1963 internal Chevrolet memo from Vince Piggins, 20 Mark II 427s were built. It’s doubtful that all were complete and running. Smokey never returned one to GM for disposal. After his 1986 shop auction, the Mark II 427 went into collector-racer Tom McIntyre’s Silver Blue lightweight Z06. It’s the very same car that finished Third at the 1963 Grand American Cup! Power output of the Mark II 427 varies from 500 to 600-plus horsepower.

MARK II - CHEVY’S MYSTERIOUS 427!Regardless of actual output, it is a living legend from the golden era of performance when GM wasn’t racing! This story was originally published in DAY ONE, that showcases the history of Motown Muscle, 1962-1974,