Chevy Big Blocks W series – 1st Gen-2nd Gen-the “mystery motor”


The 409 (6.7 L) is Chevy’s big power engine from ’61 to ’65 basically available during that time with an entry level one barrel up to two four barrel Carburetors to choose from. This variation of the “W” series is introduced in an Impala SS on December 17, 1960. The power plant’s bore and stroke have been increased and this version delivers 360 hp (268 kW) with a Carter AFB four barrel mounted on the intake. The same engine in 1962 is producing one hp (409 hp or 283 kW) per cubic inch displacement sporting dual Carter AFB carburetors now mounted on an aluminum intake manifold also with the crankshaft upgraded to a forged steel one. The same carburetor and intake set-up in 1963 will deliver 425 hp (317 kW) at 6200 rpm with a new solid lifer camshaft and a higher 11.25:1 compression ratio. This “W” version is the only big block power option until mid-1965 and became something to sing about with the release of the Beach Boys song “409” as a memorial to the engine of many faces. In summer of ’65 the new 396 cu in (317 kW) Mark IV big block “W” engine is offered alongside the 409. The 396 will produce 425 hp (317 kW) with the latest 409 now delivering 340 hp (254 kW) with a hydraulic lifter camshaft and a single four barrel 4GC Rochester square-bored carburetor on a cast iron intake.


Enter the special 427 cu in (7.0 L) engine variation of the “W” series in 1963 under the hood of an Impala sport coupe. This was available as an RPO (Regular Production Order) for drag racing only and features a cowl-induction air intake system. This rare vehicle has many aluminum body panels and the engine is aluminum as well. The 427 is a modification of the earlier 409 “W” series engine unlike later 427 power plants. It has a long stroke of 3.95” (100 mm) with a 13.5:1 compression ratio. There is a high rise two piece aluminum intake mounted on the block with dual Carter AFB carburetors delivering the fuel and this combination develops an under rated 430 hp (320 kW) and will deliver 575 ft-lb. (780 Nm) of torque. These 50 RPO Z11 Impala’s were assembled at the Flint plant and there are GM documents that insinuate up to another 50 were made at GM Tonawanda. The paperwork shows another 20 engines were shipped unassembled for parts bin stock but it is doubtful that any more than 57 units were ever wholly completed.

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The “W” 427 engine variation was the mystery motor installed in stock cars which set and broke records at Daytona Beach in ’63. The secret engine was released as the Mark IV in summer ’65 although GM sales brochures refer to it as the “Turbo-Jet V8”

Other than the ZL1 variation a torque rating of 460 lb-ft (620 Nm) is on all the Chevy 427 engines offered optionally in the Corvette, Chevelle, Camaro, Nova Monte Carlo, and the whole of the full size platform. The 1965 model year the horse power ratings are 375 ((280kW) and 425 (317 kW). For 1966 only a 360 hp (270 kW) option is also available. From 1966 through 1970 the 427 delivers 325 hp (242 kW), 350 hp (260 kW), 260 hp (270 kW), and 375 hp (280 kW). In 1969 only there is a 265 horse power (198 kW) variation of the 427 added to the list.             to be  continued…

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