The engine was switched to the 75 bhp (56 kW) 1296 cc version in April 1967, just one month after the Spitfire itself had undergone the same upgrade,[3] the revised model being identified as the GT4S 1300.

[4] At the same time the front disc brakes were enlarged and the design of the rear suspension (one component not carried over unmodified from the Triumph Spitfire) received "attention".

[4] The GT4S was joined by the 2-litre GT with a larger smoother body directly before the London Motor Show in October 1967.

[5] This model was based on the similar Triumph Vitesse chassis and used its 1998 cc 95 bhp (71 kW) six-cylinder engine.

Horsepower and suspension improvements were made in line with Triumph's Mark 2 upgrade of the Vitesse in Autumn 1968, and the convertible was introduced at the same time.