GMC Supercharger – Pulpaddict

Hemmings Motor News’ Mike McNessor does a deep dive on SUPERCHARGING BOOSTS FREE HORSEPOWER, starting in 1906!

When you discuss maximizing an engine’s volumetric efficiency, you are: –Boring everybody else at the party (as usual);

–Explaining to your spouse why it’s crucial that you drop a couple of grand on a supercharger for your sports car;

–Engaging in a 100-plus-year-old quest to get the most out of an internal combustion engine.

If you said all of the above, you’d be correct.

Supercharging was the earliest method used to squeeze more air into an engine than atmospheric pressure could provide naturally — a key to increasing an engine’s volumetric efficiency. Without the pumping action of the supercharger to increase the air pressure and density beyond the level of the atmosphere, the cylinders can’t fill to their maximum volume. But with the aid of a supercharger, they fill to the brim with a pressurized air/fuel charge. Thus, the cylinder displacement “grows” or is at least fully utilized. There is no doubt that SUPERCHARGING BOOSTS FREE HORSEPOWER! Pacers’ Tasmanian Devil Fuel Altered, with GMC/Roots blown & injected Hemi, above.

By harnessing a device that can push more air into an engine, you can add more fuel, make more power, and, voilà, you’re off to the races — literally in the case of the pioneering Chadwick Six (more about that in a moment). Giants and founding fathers of internal combustion recognized this. Rudolf Diesel was an early adopter, as were Louis Renault and Gottlieb Daimler.

In the U.S., the earliest recorded supercharged competition car started to take shape in 1906. According to a 1976 story in Special Interest Autos, it was that year that John Thomas Nicholls, chief engineer of the Chadwick Engineering Works in Pottstown, Pennsylvania, installed a belt-driven blower on a 1,141-cubic-inch Chadwick six-cylinder engine.

This early centrifugal supercharger was reportedly 10 inches in diameter, and its impeller spun at approximately 20,000 rpm while the massive six thumped along at its 2,200 redline. In 1907, Nicholls upped the boost by running three centrifugal superchargers in series. This three-stage arrangement used impellers with 12 blades each, 10 inches in diameter, each feeding into ducts of progressively smaller diameter.

Chadwick campaigned its supercharged “Big Six” in the 1908 Vanderbilt Cup Race and, according to the October 29, 1908, edition of “The New York Times,” the vehicle “… showed exceptional speed both in practice and in the early part of the race.” Magneto trouble sidelined the Chadwick, according to “The NYT,” but they speculated that it would’ve likely challenged Locomobile for the overall. Hill climbing seemed to be the supercharged engine’s forte, and the Chadwick went on to win the 1908 Wilkes-Barre Hill Climb in Pennsylvania.

In discussing SUPERCHARGING BOOSTS FREE HORSEPOWER, McNessor focuses on the following types of superchargers: AXIAL-FLOW, CENTRIFUGAL, below, ROOTS, right, ROTARY SCREW, and VANE-TYPE, above. Hot rodders and drag racers are probably most familiar with Roots-type positive displacement blowers, while vintage and classic car enthusiasts can relate to centrifugal, vane-type, and even the iconic Latham axial-flow superchargers.

Continue reading SUPERCHARGING BOOSTS FREE HORSEPOWER @https://www.hemmings.com/stories/some-of-historys-greatest-performance-legacies-were-built-on-boost/

Built on a shortened prototype ’62 Pontiac Tempest convertible, the PONTIAC TEMPEST MONTE CARLO was a hit at auto shows and major road racing events. It shared the spotlight with GM design chief, William Mitchell’s Corvair Sebring Spyder.

One thing was a given at GM in the 1960s. Chevy’s Corvette was a sacred cow and no other division could bring a two-seat sports car to market. The only way Buick, Pontiac, Oldsmobile or Cadillac could reveal branded two-seat, high-performance sporty vehicles was to have Mitchell’s GM Design create Concepts that became part of GM’s traveling auto show displays. The PONTIAC TEMPEST MONTE CARLO

two-seater, powered by a supercharged 195 cubic-inch Four rated at 250-300 horsepower, featured 15-inch- shortened unibody architecture with four-wheel independent suspension. With a wheelbase of 97 inches and overall length of 175 inches, it had a five-inch- shorter wheelbase and was almost two inches shorter overall than a ’62 Corvette!

Pontiac already had a relationship with Mickey Thompson, having supplied him with four- and eight-cylinder engines for some of his high profile, multiple-engine Bonneville and drag racing cars. Thompson came up with a supercharger package for the Tempest Four, incorporating a modified GMC 3-71 Roots-type blower driven by a two-inch-wide ribbed Gilmer belt and a manifold with a huge built-in pop-off valve. An offset adapter allowed for installing a Carter four-barrel. As with most GM showcars, the PONTIAC TEMPEST MONTE CARLO engine received abundant chrome and polished aluminum accessories.

A 15-inch section was removed from the four-passenger Tempest, converting it into a sporty two-seater. The Tempest’s four-wheel-independent suspension was retained, though the controversial flexy shaft between the engine and the rear-mounted, Corvair-based four-speed was shortened considerably, making the drivetrain more efficient.

Since Pontiac’s plan included showing the Monte Carlo at major sports car races, it was treated to a full complement of gauges, racing mirrors, dual thin blue racing stripes, tri-spoke steering wheel, hood louvers and Firestone Super Sport tires mounted on polished Halibrand knock-offs.

Wholly impractical but responsible for drawing a crowd wherever the Monte Carlo was displayed, the severely chopped wraparound plexiglass windscreen looked as though it had come off a full-tilt racecar. It offered absolutely no protection, but tied in nicely with the slick fiberglass tonneau cover with headrest fairings.

Finished in White Pearl, the Monte Carlo was also shown in 1962. The only change was knock-off wire wheels with Goodyear Blue Streak tires in place of the Halibrand-Firestone combo. Unlike most Concept/Show cars, the Monte Carlo was not crushed after it was retired. It was gifted to Ed Cole, Vice-President and head of GM’s Car & Truck Group. Before taking delivery, he had the Monte Carlo re-powered with a stock 215-inch aluminum V8. The windscreen was replaced with a production Tempest windshield; they also added a small ragtop.

The net result was a somewhat awkward looking, short-wheelbase Tempest with an oversize top. The Tempest survived and is currently in a private collection. But Mitchell’s original PONTIAC TEMPEST MONTE CARLO styling did not!