crc (04/12/83)
It is obvious to the casual observer that the Triumph GT6 engine is an underbored Tr6 motor. This is not the case. The engine was originally a four cylinder engine of about 900cc displacement. In the fullness of time triumph bored out the engine and added two cylinders, making a 2000cc six. This engine was use in "high" status triumph sedans. When Triumph decided to increase the performance of the Tr* model line, they dumped the venerable Tr2/3/4/4a 2.1 liter four and designed a new, more powerful engine. Well, it wasn't very new, and it wasn't very powerful. They decided to expand the 2000cc six. There was no more space between the cylinders to bore out the engine, so they stroked it. Of course, the entire world (except for the Soviet Union and the United States) was turning to short stroke (over square) engines because they could rev higher with less vibration. Triumph had to increase the width of the bottom of the crank case to accommodate the bigger crankshaft. The new engine with two strombergs produced about 106 horsepower, the older Tr2/3/4/4a engine about 100 hp. The new engine was smoother and did rev better than the old four. At this point the United States enacted air pollution laws. Triumph, feeling that if the US wanted to make special laws about cars could make due with special cars. They built two different cars to replace the Tr4a. The world would get the Tr5 with the new 2.5 liter six with Lucas fuel injection and 150 hp and a 3.45 rear end ratio for high speed cruising. The jerks in the US would get the Tr250 with the new six with 2 stromberg carbs, 106 hp, and a 3.7 rear end (so people wouldn't mistake it for a paper weight). The Tr250 was no faster than the Tr4a it replaced; The Tr5 was. When the Tr5 and Tr250 were replaced, the US got the Tr6 and the world got the Tr6PI (Petrol Injection). The final irony is that Triumph built 100,000 Tr250s and Tr6s, and 5000 Tr5s and Tr6PIs. More information can be found in Graham Robinson's "The Triumph TRs (updated)". Charles Colbert