Interest in the use of gas turbines as an alternative to the piston engine had been gaining support in the automobile industry during the 1960s. Chrysler had begun testing in the 1950s and began leasing their Turbine Car to the public in 1963, while British manufacturer Rover and racing team BRM combined to build a racing car for the 24 Hours of Le Mans in 1963 and 1965. These earlier turbine cars showed reliability but were unable to win at Le Mans. By 1967, team owner and car developer Andy Granatelli had created the STP-Paxton Turbocar for the Indianapolis 500, which also faced mechanical issues despite leading the race.
At the same time as Granatelli's turbine debut at Indy, racer Ray Heppenstall began to conceive a design for his own sports car to make use of a gas turbine, improving in some areas where the Rover-BRM had failed several years before. Heppenstall felt that a more simplified design for the chassis could make a turbine-powered car more competitive. Heppenstall originally proposed the car to Allison Engine Company and later to Williams Research. He eventually turned to fellow racer Tom Fleming for aid, who was at the time vice-president of Howmet Corporation, which provided castings for turbines in the aerospace industry. Heppenstall and Fleming were able to convince Howmet that backing a competitive and unique sports car could promote public awareness of the company. Howmet agreed to fund the project, lending their name to the car.
Heppenstall began the project by purchasing a Cooper Monaco sports car, but later decided it was not the best choice for a turbine and the car was sold off. Bob McKee, owner of McKee Engineering, was then contracted by Heppenstall to build two cars brand new. The first space frame chassis was adapted from an older McKee car initially built for the Can Am series in 1966, while the second chassis was built from scratch, allowing it to be purposely designed around the use of a turbine engine, including a chassis 2.25 inches (57 mm) longer. The chassis were known as the Mk.9 to McKee, but only ever raced as turbines under the Howmet TX guise.
The Mk.9 was designed around the FIA's Group 6 regulations for sports prototypes, allowing for a completely custom mid-engine layout. Closed cockpit bodywork with gullwing doors was designed by Bob McKee to shroud the mid-engine layout. Standard double wishbone suspension with coil springs were used with disc brakes on each wheel. A 32-US-gallon (120 L) fuel tank was placed between the cockpit and turbine, housing Jet A fuel.
The turbines to power the two Howmet TXs were leased from Continental Aviation & Engineering. The TS325-1 gas turbines were prototypes from an aborted bid for a military helicopter contract. The loaned turbines weighed 170 pounds (77 kg) and were able to provide 350 bhp (260 kW) and 650 lbf⋅ft (880 N⋅m) of torque. A maximum of 57,000 rpm was able to be reached.
A two-stage setup used an internal power turbine to drive the rear wheels through the use of reduction gearing. Due to the wide variable output of the turbine and the high level of torque, a standard gearbox was not necessary, leaving the Howmet TX with only a single gearing speed. However, the gearing ratios were able to be quickly changed in the differential, allowing the car to be adapted to various circuits. Due to the use of a single-speed transmission, there was no gearing for reverse. Although Heppenstall initially wished to do without reverse, the FIA mandated its use and a small electric motor powered by the turbine was installed, allowing the car to move in reverse.
The turbine itself used two large exhaust pipes. However, a third pipe was situated off-center for use with a wastegate. The wastegate was designed to eliminate the lag between the driver pressing the accelerator and the turbine increasing its revolutions. Once the turbine was at its maximum revolutions, the wastegate helped regulate the flow of hot gas from the core to the power-turbine, thus increasing or decreasing the power output to the gearbox.
The FIA used an equivalence formula to determine the Continental TS325-1's displacement of 2,960 cubic centimetres (181 cu in), allowing the Howmet to compete in the Prototype Under 3000 cc category.
Following completion of the two Howmet TXs, the cars were brought to the 24 Hours of Daytona, the opening round of the 1968 International Championship for Makes. Before even entering competition the TX earned attention, and was featured prominently on the race program. Although both cars were in attendance, only the newer car was entered in the race; the other car was kept as a spare. The driving team of Heppenstall, Dick Thompson, and Ed Lowther qualified with a lap time seventh fastest overall. Several competitors made early refueling stops allowing the Howmet to improve to third place but on lap 34 the turbine wastegate failed to reopen, causing the car to crash.
By the 12 Hours of Sebring a few weeks later, the TX was able to improve its pace, this time qualifying third. The turbine ran reliably at first but, as the race continued, debris damaged the turbine and caused it to shake loose from its mounts. The TX was eventually retired after six hours. Following Sebring, the International Championship returned to Europe, and the Howmet team followed. They entered the BOAC 500 at Brands Hatch, but suffered a crash after only seven laps due to wastegate problems. Staying in England, the Howmet team entered a national sprint race at Oulton Park, but a starter motor failure during a pit stop prevented the car from finishing.
The TX returned to the United States to contest the SCCA National Championship. The car finished second at the Vandergraft Trophy in New Cumberland, West Virginia, setting a new lap record for the circuit. Following a retirement in Michigan, the TX next arrived at the Heart of Dixie event in Huntsville, Alabama. The Howmet TX won both the qualifying sprint and the main event. These two victories marked the first-ever wins by a turbine-powered car in a racing event.
Howmet decided in 1969 that although the racing program was too expensive to continue, the two cars it owned could still be put to promotional use. Heppenstall repaired the second TX chassis (#GTP2) and adapted it with open-cockpit bodywork, earning it the name Howmet TX Mk.II. The new vehicle attempted to break world land speed records for turbine-powered cars. The TX Mk.II set six records recognized by the FIA, with timing recorded by the International Motor Sports Association (IMSA).
In 1971, Howmet ended their promotional use of the two TX cars. The two chassis were sold to Ray Heppenstall for one dollar, but the Continental turbines had to be returned. Heppenstall eventually sold the two chassis. Chassis #GTP1 was bought by Jim Brucker and restored with an original Continental turbine. Following restoration, #GTP1 won the Sebring Trophy at the 2007 Amelia Island Concours d'Elegance. The second car, chassis #GTP2, was restored to its original closed-cockpit configuration but utilizes an Allison 250C18 turbine. A third frame, #GTP3, was later completed to original specifications, also using an Allison unit. The different powerplant required some redesign, as the exhaust was now vented out of the top of the engine cover instead of out the rear of the car. #GTP3 does not have the wastegate system.
This article is based on information from the Wikipedia article "Howmet TX". No external sources were consulted.
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