A Spitfire with the Vitesse’s six under a fastback — and three different rear ends across three marks.
The GT6 is a fastback coupe on Spitfire underpinnings with the Vitesse’s 1,998cc straight six in the nose. Bodyshell, bonnet, front springs, brakes and differential are all uprated for the heavier engine, so treat Spitfire overlap as case-by-case rather than automatic. The Mk1 of 1966 carried the Spitfire swing axle and was heavily criticised for it — at its worst lifting a wheel mid-corner on a closed throttle. 15,818 were built.
Then the rear end changed twice, and the second change is the one people miss. The Mk2 of 1968 fitted reversed lower wishbones and Rotoflex rubber driveshaft couplings — the same fix the Vitesse Mk2 got at the same moment, and the good one. 12,066 built. The Mk3 of October 1970 started on that same Rotoflex setup, then in 1973, near the end of production, switched to the cheaper swing-spring layout from the Spitfire Mk IV, with a larger front anti-roll bar to make up for the reduced rear roll stiffness. So an early Mk3 and a late Mk3 have entirely different rear ends, and the parts do not cross. No source gives a chassis number for the change, so the car has to be looked at.
Triumph GT6 — specification & changes within the model
- Mk1
- 1966 – September 1968. 1,998cc straight six, 95bhp. 15,818 built. Spitfire swing-axle rear — heavily criticised.
- Mk2
- 1968 – December 1970, GT6+ in America. 104bhp. 12,066 built. Reversed lower wishbones and Rotoflex couplings — the same fix as the Vitesse Mk2, at the same time.
- Mk3
- October 1970 – December 1973. 104bhp. 13,042 built. Started on the Mk2 Rotoflex rear, then changed in 1973 to the Spitfire Mk IV swing spring, with a larger front anti-roll bar to compensate.
- The Mk3 trap
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An early Mk3 and a late Mk3 have entirely different rear suspensions. No chassis number is documented for the change — look under the car before ordering rear springs, driveshafts or couplings.
- Engine
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The Vitesse 2-litre straight six, not a Spitfire unit. Ancillaries cross with the Vitesse and the Triumph 2000.
- Shared with the Spitfire
- The backbone chassis family and the Michelotti body origins. But bodyshell, bonnet, front springs, brakes and differential are uprated for the six — check each group rather than assuming.
- Rotoflex couplings
- A wear item, and specific to the Mk2 and early Mk3. They do not fit a swing-spring car and a swing-spring car does not need them.
