The Triumph Six Cylinder or Triumph I6 engine is a cast-iron overhead valve straight-six engine produced by Standard Triumph. It is an evolution of the Standard Motor Company's inline-4 Standard Eight, with the addition of two cylinders and a larger displacement. Introduced in their Standard Vanguard Six in 1960, it was used in a wide range of Triumph vehicles, including the Triumph TR5, TR250, and TR6.