The early '60s produced a period of unique and optimistic automotive engineering. Rival powerplants were engaged in another horsepower race, gasoline remained cheap, and automakers were relatively free from governmental regulation.

Automotive researchers received the corporate interest, funding, and freedom to take seriously radical alternatives with regards to future automotive and truck platform powerplants. Though several options to the piston engine were studied, one of the most promising was the gas turbine engine.

American manufacturers, including Caterpillar, Chrysler, Detroit Diesel, Ford, and International, were engaged in the development of turbines, regarded then as the future alternative for the gasoline-powered piston engine. Each of these corporations had a series of running prototypes in production test beds for ongoing evaluation. All shared common internals but varied in size and weight depending on market application, platform type, and torque and horsepower output. General Motors had developed several operational turbine concept platforms in the early '50s, Chrysler began the research and market interest in 1939, and Chevrolet, Ford, and International directed productive efforts toward the fullsize truck and heavy-duty market.

The industries' shared opinion was that this new powerplant would provide performance and control equal or superior to the piston powerplants, be notably smoother at all rpms, have greater operational range with less component fatigue, start easier in colder climates, and provide instant heat and window defrosting on colder days. Turbines, it was also thought, would deliver equal or superior fuel mileage, provide longer unit life at less cost, require less maintenance, reduce or eliminate periodic oil changes, and make the antique cooling system, with its accompanying annual antifreeze replacement, obsolete. In short, a futuristic powerplant providing greater efficiency, using a variety of common liquid fuels, free from expensively refined petro-octane varieties, combined with cleaner exhaust.

Back Ground
In July of 1965, Chevrolet announced its Turbo-Titan III, an operational prototype combining advanced truck styling with novel features, including major design improvements within its fifth generation gas turbine engine. Installed on an existing production truck chassis, and including a specially produced 40-foot stainless trailer, the entire platform had a 50-foot overall length and an operating gross combination weight of 76,800 pounds.

The GT-309 turbine engine was based on more than 15 years of continued development. Its operating heritage included units used in the experimental Firebirds, the Turbo-Cruiser bus, two Chevrolet Turbo-Titan production truck platforms, and 15 operational Allison Prototypes. The 309 produced 280 hp with an upper shaft speed of 4,000 rpm, reduction geared downward from 35,000 rpm. Because turbine engines deliver their highest torque levels at stall, the 309 developed a maximum torque rating of 875 lb-ft at idle. Thus, the colder the climate, the more instant power was available.

The 309 used the uniform basic internal components as its cousins, including a compressor, a gasifier, a power turbine, and a regenerator. The gasifier was mounted on the same shaft as the compressor. The power turbine gear was connected to the output shaft. Incoming air was drawn in by the compressor, compressed, and directed to the combustion chamber. This compressed air, combined with fuel sprayed into the chamber, generated combustion with operating temperatures of 1,700 degrees Fahrenheit. These gases, under high pressure and temperature, flowed through nozzles against the vanes in the gasifier unit, driving both the turbine and compressor at 35,700 rpm. This power turbine, though located at the rear of the gasifier, was not connected to it.

After moving through the gasifier unit, the nozzles directed the gases toward the turbine blades, moving them from stall to 35,000 rpm. All of the above internals were fitted into two divided chambers: the high-pressure plenum, containing the combustion chamber in front, with the lower pressure exhaust plenum in the rear. Located in the passage between these cavities were the turbines. The heated air passed through the combustion chamber, was combined with the fuel, which drove the turbine units, and exhausted into the low-pressure unit. The gases were cooled as they made their way through the regenerator, which transferred the heat combined with fresh incoming air to the high-pressure plenum. In short, a continued process.

The gas temperature emitted by the 309 averaged 1,200 degrees. The regenerator absorbed the heat and dropped these temperatures in half to the 300-500 degree range, about half of a conventional diesel unit. More than 90 percent of the exhaust system heat was salvaged, which reduced the amount of fuel needed to produce the high velocity gas needed to drive the turbines. The regenerator also eliminated the need for mufflers and a conventional exhaust system, serving as an insulating blanket for heat and noise.