Howmet TX - Development - Turbine

Turbine

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 which Continental was not putting to use at the time. 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 amount of fuel actually entering the turbine, thus increasing or decreasing the power output.

Although turbines cannot have their displacement measured in the same way as a piston engine, the FIA used an equivalence formula to determine the Continental TS325-1's displacement of 2,960 cubic centimetres (181 cu in), although Heppenstall has since admitted that the engine was actually above the three litre limit. This allowed the Howmet to compete in the Prototype Under 3000 cc category of the Group 6 formula.