Chevy W-series Big-Block
Anyone accustomed to conventional 90-degree V-8s will freak out upon tearing apart a W-series big-block Chevy for the first time. Introduced in 1958 as the precursor to the Mark IV big-block, it incorporated many unique design elements. Instead of machining traditional combustion chambers into the cylinder heads, Chevy cut the deck surface of the block at a 74-degree angle to the cylinder bore centerline. In other words, the engine-mount side of the block was taller than the lifter valley side of the block. This lopsided deck surface, in conjunction with piston crowns that sloped sharply downward toward the outside of the block, created a wedge-shaped combustion chamber at the top of the cylinder, in the block itself. This arrangement was said to improve quench, flame front travel, and cylinder pressure to maximize low-end torque.
Whether their unique combustion chamber design accomplished that mission is up for debate, but what's certain is that the W-series big-blocks ran hard. Launched in '58, the 348 featured a 4.125-inch bore, and a 3.250-inch stroke. With an optional mechanical lifter camshaft and three two-barrel carbs, it produced 350 hp. By '61, Chevy replaced it with the 409, which used a larger 4.312-inch bore and a 3.500-inch stroke. The most potent version of this engine was released in '63, which produced 425 hp, thanks to a solid-lifter cam, dual four-barrel carbs, and an 11.25:1 compression ratio. GM also built a 427ci W-series engine as a drag race package, which was essentially a 409 with a longer 3.650-inch stroke, 13.5:1 compression, and a high-rise intake manifold. The 427 was conservatively rated at 430 hp, and it's believed that only 50 of them were built.
Taking into account that it was designed in the '50s, the fact that the 348, 409, and 427 each had variants that made 1 hp per cubic inch is very impressive. As racers pushed these engines to the limits, however, the heavy pistons necessary to achieve their odd combustion chamber design often led to connecting rod failure and severe engine damage. Furthermore, the in-block chambers reportedly reduced power above 6,000 rpm, prompting GM to replace the W-series engines with the Mark IV big-block. That said, the legacy of the W-series platform is that it served as the foundation for what would eventually evolve into one of the most mystical and powerful race engine platforms of all time, the Mark IV big-block Chevy
"...the heavy pistons necessary to achieve their odd combustion chamber design often led to connecting rod failure..."
Pontiac Cammer Straight-Six
These days, 300-plus horsepower six-cylinder engines are becoming the norm, offered by both domestic and foreign manufacturers. In many respects, a little-known Pontiac motor came close to offering V-8 performance in a six-cylinder package long before the current engines were conceived. As the head of Pontiac's Advanced Engineering team in the '60s, John DeLorean spearheaded a high-tech straight-six prototype engine that was equipped with a beltdrive SOHC. The late '50s had seen a sharp recession, and Pontiac was rolling the dice on the resurgence of fuel-efficient six-cylinder engines. By '61, DeLorean was wrist-deep in the project, intrigued by the promise of OHC valve actuation. He was inspired by OHC straight-sixes of the day offered by Mercedes, Alfa Romeo, and Jaguar for their balance of power and fuel economy.
Based on the Chevy OHV straight-six, Pontiac's cammer used a 3.850-inch bore and a 3.250-inch stroke for a total of 230 ci. While it shared the crank and rods with the Chevy engine, Pontiac cast its own block that extended the skirt 2.4 inches for improved rigidity. On the top end, the Pontiac six used large 1.920-/1.600-inch valves, actuated by a cam mounted in the valve covers. To cut down on valvetrain noise that was common with OHC engines, the Pontiac cammer was equipped with hydraulic lifters and a rubber timing belt in lieu of a chain. Rated at 165 hp, the Pontiac straight-six went into production in the '66 Tempest. A hopped-up version-equipped with a bigger cam, 10.5:1 compression, and a four-barrel carb-was offered as well, rated at 215 hp and 240 lb-ft of torque. The cammer six was also available in the '67-69 Firebird.
Its promise and potential aside, due to the high production costs of the Pontiac OHC straight-six, most buyers opted for V-8s instead, and GM dropped it following the '69 model year. Nonetheless, it's not a stretch to surmise that it served as a precursor to the potent OHC six-cylinder engines that power the new Camaro and Trailblazer. Furthermore, Pontiac engineers incorporated many of the design elements of the cammer six into prototype DOHC 389 V-8s intended for use in NASCAR. GM's corporate ban on racing prevented this engine from ever seeing competition, but it's rumored to have produced more than 500 hp.