[3] The TX later set six Fédération Internationale de l'Automobile (FIA) land speed records for turbines after being retired from racing.

The car nearly won the race driven by Parnelli Jones, but suffered a mechanical failure after leading over two-thirds of the event.

Heppenstall and Fleming were able to convince Howmet that their backing of a competitive and unique sports car could promote public awareness of the company.

[5][8] The second car #GTP2 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.

[8] The Mk.9 was designed around the FIA's Group 6 regulations for sports prototypes, allowing for a completely custom mid-engine layout that was only limited in terms of engine sizes available to competitors.

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.

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.

[5] 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.

[2] The driving team of Heppenstall, Dick Thompson, and Ed Lowther qualified with a lap time seventh fastest overall.

[11] Several competitors made early refueling stops allowing the Howmet to improve to third place but on lap 34 the turbine wastegate failed to reopen, giving the driver too much power for the corner he was in.

[5][13] Staying in England, the Howmet team entered a national sprint race at Oulton Park for English driver Hugh Dibley.

Closer to home, the problems with the experimental TX were able to be overcome as the car finished its first race, the Vandergraft Trophy in New Cumberland, West Virginia.

Once again the car won the short qualifying race to earn pole position and went on to lead every lap of the main event, winning by an eleven-lap margin.

[3][5] Feeling that the TX was now capable of taking on European entries, both TXs were entered in the 6 Hours of Watkins Glen, another round of the International Championship.

[7] The same drivers were assigned to the cars, but their qualifying performance at the Circuit de la Sarthe was hampered by the long straights.

The fuel system was not providing enough Jet A to the turbine to allow it to produce its full power output, meaning the car had to limp down the circuit's long straights.

[2] While that car continued at a slowed pace, the other suffered a wheel bearing failure two hours later, requiring a lengthy three-hour repair.

By the sixth hour of the event the car was disqualified by race officials, having covered an insufficient distance of only 60 laps.

With the 1968 season over, Heppenstall planned for the following year, including the development of a new multi-gear transmission to replace the single speed unit.

With the TX Mk.II weighing approximately 1,000 kilograms (2,200 lb), the car was able to make attempts at two classes of records thanks to the addition or subtraction of ballast.

[14] The second car, chassis #GTP2, was converted from its open-cockpit bodywork back into its original closed-cockpit design in a restoration carried out by McKee Engineering at the behest of new owner Chuck Haines.