Controversy surrounds the Mystery Motor that used to stomp the field in the first 100 mile qualifying race at the 1963 Day - tona 500. Driving Ray Fox’s 1963 Chevrolet Impala Johnson displayed blistering speed in qualifying and in the race; proving the combination fast and formidable while exceeded 168 mph on some prac - tice laps. When dominated the second 100 mile qualifier with another mystery motor in Smokey Yunick’s car competitors nearly lost their minds. Three other mystery powered qualified for the race and all five cars exceeded the previous years qualifying speed by seven to ten mph. Chevrolets swept both of the100 mile qualifying races, but ultimately failed to win the 500 due to various mechanical difficulties. Still, proportions; sometimes too much. The Mystery their speed was staggering and everyone wanted Motor is a case in point. Legend and lore abound, to know how they did it. particularly on the internet making it difficult to clar - ify the Mystery Motor’s content and performance as Present day fascination with the nostalgic glory of it relates to subsequent Mark IV production en - the muscle car years has clouded our memory of gines. So called internet forum “experts” claim that events, cars and engines of that era to near epic the engine was just a bored out 409 with a Z11

Junior Johnson 1963 Johnny Rutherford 1963 Daytona 500 lower end and the newly designed “porcupine” cylinder heads. This theory completely ignores the obvious problem of deck angle and combustion chamber mismatch. Someone is always surfacing with a story about a long lost uncle who actually worked in the dyno room or the design shop and he just happened to tell his pharmacist who then told his pastor who told a friend who passed along that there were only eighteen motors and they were a special mix of W-motor specs and secret new tech - nology. Well, maybe not.

The Mark II Mystery Motor was designed by Dick Keinath, a brilliant engineer who at one time held every job in the Chevrolet engineering group from 2-inch cast iron exhaust manifolds draftsman to Chief Engineer. He worked on the orig - inal small block with Ed Cole and Ed Kelly develop - bores the farther they opened. This improved flow ing an all aluminum small block V8. He did the and subsequent cylinder filling by unshrouding the original development work on the 348 and 409 cylin - valves. The block was all new, adopting nothing der heads and had primary responsibility for the 409 more than the basic location of the W-motor’s main engine. As such he is factually the father of all oil gallery, the same 4.84-inch bore centers and the Chevrolet big blocks. Truth be told, Dick Keinath had same size main saddles. a hand in every modern Chevrolet engine from four cylinders to early 348 NASCAR engines to 302 Z28 Few people know that there were three versions of engines and of course the now legendary big blocks. the Mystery Motor. It was originally designed, built and developed as an “all new” 409ci engine to cap - With Ford sporting 427ci big blocks and Chrysler italize on the existing 409’s robust reputation. fielding 426 cubic inches Chevrolet’s 427 Mystery Keinath explains that the only thing even closely re - Motor was the logical choice to compete with them. sembling the W-motor design was the crankshaft. The big mystery of course was the cylinder head The mystery engine began as a 409ci engine design which incorporated large canted valves that based on the all new Mark II cylinder block and moved away from the chamber walls and cylinder heads. It utilized a 409 crankshaft and bearings;

Mark Main Main Rod Rod Series CID Caps Bore Stroke Journal Journal Length Valves

II* 409 2-bolt 4.3125 3.500 2.4990 2.2000 6.135 2.19/1.72 IIS 427 2-bolt 4.3125 3.650 2.4990 2.2000 6.135 2.19/1.72 IIS** 396 2-bolt 4.3125 3.390 2.4990 2.2000 6.135 2.19/1.72

S = Stroked * Development engines, pre-November 1962 ** Development engines, mid-1963, tested but never raced Note: No adequate records exist to indicate exactly how many of each displacement were built. The 427ci version was the only one ever raced.

nothing else. That means Mark II big block engines terial for adjacent head bolts. Unique cast iron have smaller main bearings than the follow-on Mark pushrod guide plates were mounted with short bolts IV versions. Keinath states that the Mark II also had above the intake ports (see photos). Cast iron ex - a 4-5/16-inch bore (4.3125) and a 3.500-inch stroke haust manifolds featured 2-inch unequal length pri - (same as the 409). It was a NASCAR intended rac - maries. Four different 180° hi-rise intake manifolds ing engine designed to replace the 409 and the dis - were designed each with subtle revisions to accom - placement was retained to extend the benefits of modate the different displacement versions of the the 409’s notoriety. Mark II engine.

Most of the testing and development was done with From his testing experience Smokey Yunick believed 409ci versions. Development engineers were able that the best one was casting number 0-233239, but to generate the required power at that displacement, it is unknown which engine this one worked best on. but in October of ‘62 negotiations with NASCAR re - Speculation suggests the 427, but its power was sulted in approval to enlarge it to 427ci to gain parity subsequently matched by the 396ci version so it’s with Ford and Chrysler. A mad rush ensued to de - anybody’s guess until someone who has one of the sign longer 3.65-inch stroke crankshafts that were remaining engines decides to pull a head to check similar, but subtly different to the previous 409 stroke length and match up the casting numbers. based cranks. This development package became Smokey was also dissatisfied with the2-bolt mains known as the Mark IIS (for stroked) and the new that came on all Mark II engines. There were no 4- cranks eliminated the 409 crank from the package. bolt versions, but Smokey devised his own main cap The engines that ran at Daytona were 427ci Mark brace that bolted onto the 2-bolt caps and was se - IIS versions. Later on, 396ci versions were also de - cured to the main webs by two additional bolts to veloped but never raced. form sort of semi-4-bolt man caps. Mark II camshafts also had the grooved rear cam journal characteristic According to Keinath, the W-motor was designed of early (1965-66) Mark IV engines and they still in - from the get go as a big truck engine that evolved corporated a canister type oil filter. to a racing engine because there was nothing else available. Designers saw what was wrong with it Retired Mystery Motor test and development engi - and switched strategies. Mark II series engines were neer Bill Howell has stated that subsequent devel - designed from the outset as racing engines (the opments saw the 427ci engine destroked to 396 Mark II Mystery Motor) and were subsequently re - cubic inches because NASCAR planned to limit dis - vised to accommodate truck and passenger car placement. The 396 version was tested by Smokey service. The difference was considerable as the new Yunick in the fall of 1963 at the Ft. Stockton, Texas Mark series was designed for much higher efficiency test track with initial plans to run the 1964 Daytona than the W-motors which they easily out-powered. 500 under the table without corporate endorse - Keinath further remarks that the Mark II and later ment. According to Howell, this version was the Mark IV series engine are externally almost identi - best performing engine of the bunch even with the cal, but that nothing really interchanges between reduction in displacement. them primarily because of revised port locations; head bolt locations, smaller mains and other revi - In his book, “Best Damn Garage in Town ”Smokey sions necessary to a production environment. Yunick offers high praise for Dick Keinath and his engine design talents. According to Smokey, 44 The cylinder heads carried 2.19/1.72-inch valves sets of parts were produced for these engines, but residing in closed style chambers and operated by Tonawanda engine plant records indicate that a 1.65:1 rockers. They had round exhaust ports with total of 60 engines were manufactured for the Mark a bump on the upper side to provide additional ma - II program. All of them had a 4.3125-inch bore and 2.5-inch main journals. By the end of the program sure to stay below 400ci. Despite this engineers 3 distinct stroke lengths had been used to achieve eventually matched the 427’s power level with both 3 different displacements as shown in the accom - the Mark II 396 and the production Mark IV 396. panying chart. Disclaimer: Production Mark IV 396 V8s (1965) required a re - The accompanying photos have circulated freely on the duction in bore size to accommodate foundry based internet with no specific credit or indicated source. They casting issues attributed to relocated head bolts were initially found on the Jalopy Journal under the H.A.M.B. section. Thanks to wrench409 for posting and coolant passages. And it required a stroke in - them. Anyone with confirming or contact information is crease to 3.76-inches to match the revised 4.094- urged to click Here To conTAcT us regarding inch bore. Main journals were also enlarged to source of these photos and contact information. We are 2.75-inch to ensure the desired durability in truck seeking more information from all owners of mystery mo- applications. Keinath also confirms that the 396 dis - tors or parts for hi-resolution press quality photos for a placement originally came about because of new book. THAnks! NASCAR limiting displacement to 6.5L about then and because there was unofficial corporate pres -

This first story on Chevrolet’s legendary mystery motor generated a lot of new questions and a few sour com - ments by desktop experts still insisting it was a revised 409 W-motor. So we decided to solicit more facts straight from the horses’ mouth.

We consulted an old friend who supervised all the test - ing and development of the mystery motor program as a young Chevrolet engineer. Having known Bill Howell for nearly four decades we felt sure we could get the straight scoop and clear up some misconceptions. We were right...