Last month we told you about GM's latest legend in the making, the all-new LT1. Already, tuners have tweaked the new C7 to run the quarter-mile in the high 9s. That's impressive untapped potential. The public's love affair with Corvette engines began with the 265ci small-block Chevy in 1955. And when the 283 fuelie launched two years later, true Corvette performance had finally arrived.
Corvette engines have proved so potent over the years that the initial offering, the so-called "Blue Flame Six," seems like an embarrassing anomaly. But to understand the significance of that engine, one must adopt the perspective of Chevrolet in 1953. The response to the '53 Motorama Corvette had been so positive, the company was keen to build a production version as quickly as possible. It wasn't about to wait around for the arrival of the new V-8 engine.
In the early 1950s, the Jaguar XK120 was regarded as one of the world's best sports cars, with a top speed of 120-plus mph, and numerous speed and endurance records to its credit. The XK120 was powered by a 3.4-liter (207ci) inline six that produced 160 hp. The six's real mojo was up top, where it employed an aluminum head with hemispherical combustion chambers, double overhead cams, and twin side-draft SU carburetors. It was quite an impressive powerplant for its day, and no one thought less of it due to its six-cylinder configuration.
Back in Detroit, automatic transmissions were still considered cutting-edge hardware. While the thought of a shiftless trans in a sports car might seem like sacrilege these days, Chevy product planners had a different outlook. They reasoned that if the Corvette came with a manual trans, the public would view the car as old fashioned. After all, went the thinking, who wants to shift gears like they did in the olden days? So, from the beginning, a manual Corvette was not a consideration. Besides, the Powerglide two-speed auto was perfectly matched to what was then known as the Powerglide six-cylinder engine.
The Powerglide six was a solid, passenger-car version of the 235ci Chevy truck engine that had been around since 1929, when it was known as the Stovebolt Six. It made 115 hp using wedge-shaped combustion chambers, hydraulic lifters, 7.5:1 compression, and a single-barrel downdraft Carter carb. The '53 version received aluminum pistons (a first for Chevy), full-pressure lubrication for the bottom end, and steel-backed inserted rod bearings.
The improved engine served as the starting point for the new Corvette mill. Compression was bumped from 7.5:1 to 8.0:1, requiring high-test gasoline. The solid lifters from the 261 truck engine were mated to a new camshaft with 0.405-inch lift for the intake and 0.414-inch lift for the exhaust—then highest lift numbers in the industry at the time. Dual valve springs were used to avoid valve float above 5,000 rpm.
To clear the Corvette's low hood, three horizontal Carter carbs were used on a special aluminum manifold. The show car had pancake-type air cleaners, but production cars used bullet-shaped units. Each carb fed a single "Siamesed" pair of intake ports, with all three connected by a small-diameter surge pipe that evened out the fuel/air flow at all speeds. A split-design exhaust manifold used separate outlets in a single casting for the front and rear sets of three cylinders; these exited into a split for the dual exhausts.
A double-action mechanical fuel pump upped the fuel pressure, and a high-efficiency water pump kept temperatures down. The ignition system had a modified breaker cam to provide longer dwell above 5,000 rpm, colder AC spark plugs, and a shield around the distributor to reduce radio interference. To handle the extra grunt, the Powerglide transmission featured higher hydraulic-line pressure, and the valve body was reset to provide automatic upshifts from First to Drive at 4,500 rpm under full throttle. Fitted with a 3.55 rear, the Corvette had a top speed of 108 mph at 4,800 rpm.
The newly rechristened Blue Flame Six produced 150 hp, making it the most powerful inline-six engine Chevy had offered to date. While not as exotic as the Jaguar's DOHC six, it was a notable accomplishment considering that the American carmaker had never built a performance engine before. Of course, no one could have anticipated the rapid development of the SBC, which would soon relegate the Blue Flame Six to the dustbin of Corvette history.