Chevy’s Mystery 427, W-Head Engines

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Workers in Junior Johnson’s garage at Daytona in 1963 get ready to install a brand new 1963 427 NASCAR Mystery Motor. (Photo courtesy Junior Johnson).

Q: Greg, you’ve mentioned the Mystery 427 Chevy engine in previous columns and I’m still confused. What really was the Mystery 427, and was it the same as the Z-11 that the drag racers ran? Is this what you are referring to? When did the Mystery engine appear in the Chevy passenger cars? Greg L., Oklahoma City, Oklahoma.

A: Greg, in 1963 the Chevy Mystery 427 NASCAR engine and the drag strip 427 Z-11 were introduced. However, these engines were completely different.

The “Mystery” engine came about under cloaks of secrecy as Chevy made available to select NASCAR teams a canted valve cylinder head, Mark II 427 “Mystery” engine back in late 1962.

These engines differed from the 409 design and featured a beefier bottom end, stronger crankshafts and better connecting rods. However, the real secret of the Mystery 427’s power came from its new closed combustion chamber canted valve “porcupine” cylinder heads, which were angled in two planes.

These new heads were similar to the old W-style 409 only in its canted valve position. The 409 style heads did not have a combustion chamber as combustion ratios came solely from different piston configurations.

According to NASCAR mandate, Chevrolet produced enough parts for 50 Mystery engines. No drag racers received this Mystery” engine.

Here’s a photo of the 427 Z-11 engine, with valve covers and heads that are 100-percent 409 style. (Chevrolet photo).

Smokey Yunick, Rex White, and the duo of Ray Fox and Junior Johnson were the main Chevy teams that received the “Mystery” Mark II 427 engines well before the 1963 Daytona 500. They knew they had something very special in their garages, but there was a “problem,” and it was spelled “NASCAR Inspection.”

Both Smokey and White admitted that perhaps 26 engines were available, not 50, which meant they had to scurry by trucking the engines back and forth to each other’s garages before NASCAR inspections, repainting them and giving the appearance of more engines. Additionally, one complete 427 Chevy Mystery engine was made available to the Holman-Moody Ford team, a gesture of “proof” that a minimum 50 engines were available according to NASCAR.

Successful in their inspection ingenuity, the Mystery 427’s got off to a great start at Daytona in ‘63. Johnny Rutherford won his first ever NASCAR race in Smokey Yunick’s Chevy in one of the Twin 100-mile qualifying races (now 150-miles), followed in second place by Rex White in another Mystery 427.

Johnson won the accompanying qualifier in his No. 3 Holly Farms Impala and won the pole with a lap of 165 and change, some 10-mph faster than the prior year. It was a clean sweep for Chevy in the prelims.

However, none of the Mystery Chevy’s did well in the 500, all falling to mechanical woes. In a top five Ford sweep, Tiny Lund in a Wood Brothers Ford won the race subbing for burned and hospitalized Marvin Panch (who Lund pulled to safety following a sports car crash).

Johnson lasted until lap 26 when his ignition failed, while Rutherford, who had a best finish for the Chevy teams at ninth, was not on the lead lap at the finish. White, who finished 14, told me head gasket problems forced him to the pits every 30 laps or so for water. He’d go out, unlap himself under green conditions, catch the leaders, and then have to come back in again for more water, losing another lap.

To make matters worse, General Motors officially announced after the Junior Johnson win at Charlotte in October of ’63 that it was pulling out of racing, leaving the Mystery motor teams high and dry. White, knowing of the rumors of a Chevy pullout early on, moved to a Bill Stroppe Mercury at mid-year. Johnson, meanwhile, won eight races in ’63 and by season’s end announced a switch to Dodge for 1964.

As for the Z-11 W-head 427, drivers like Hayden Profitt, Ronnie Sox, Malcolm Durham, Don Nicholson, Butch Leal, Hubert Platt, Wally Bell and Dave Strickler all competed on the nation’s dragstrips with Z-11 427’s. This engine was still based on the W-head 409, completely dissimilar to the Mystery engine. The option included a longer stroke crank, aluminum front end, special cowl air intake through the headlight cones and two piece aluminum intake with dual fours listed at 430 horses with 13.5 to 1 compression.

As for passenger cars, the very first “Mystery style” big blocks came in 396-inch form and appeared in 1965 in Corvette, Caprice and Chevelle models thus becoming the first true descendents of the NASCAR “Mystery 427.” The first production 427 “Mystery” style engine, renamed a Mark IV 427, appeared on a showroom floor in Impala and Corvette models in 1966.

Hope this all helps.

(Greg Zyla writes weekly for GateHouse Media, More Content Now and He welcomes reader questions at 116 Main St., Towanda, Pa. 18848 or email at    

Greg Zyla

Greg Zyla