Triumph TR6 Engine

It is a long-stroke engine with pushrod-operated overhead valves, a chain-driven camshaft and four main bearings, and its block and head are of cast iron. Classic & Sports Car explains the long stroke: the bores were siamesed, so when the capacity grew, the stroke had to grow with it. The importer's launch description of 1969 listed chrome-plated top compression rings on aluminium-alloy pistons, exhaust valves faced with Stellite, lead-indium bearing shells, and an eccentric-lobe oil pump with a full-flow filter.

Its character is its torque. Motor Sport's tester in 1971 found the TR6's engine "all too willing to exceed" its peak revs; half a century later, Classic & Sports Car found that "It hunts and splutters as you prod at the throttle" while the driver works the choke for a steady idle, and that above 4,000 rpm it gave more noise, if an enjoyable one, rather than more pull. Each engine's number carries the same prefix as the car's commission number; identification shows where to find it, and the buyers guide gives the checks.⁠source 4​source 1​source 5​source 6​source 3​source 7​source 8

Triumph's brochure explained the injection in a sentence: "fuel is pumped from the tank, pressurised and accurately metered", and the measured charges are injected into each port in turn as a fine spray. An electric pump, in the boot (trunk) beside the tank and filter, raised the pressure; a metering unit, driven from the distributor drive, shared the fuel out; and each cylinder had its own injector and throttle butterfly. The brochure sold it on its pedigree, as "a product of international motor racing".

The pump was the first thing testers noticed. In 1971 Motor Sport found that "the fuel pump made an alarming whine", and in 1973 Clive Richardson wrote that his "would have drowned the noise of Concorde"; his car needed three pumps in its first year. A reader of Motor Sport reported in 1973 that a faltering pump could be revived with a tap, and cured with new brushes like a windscreen (windshield) wiper motor's. Richardson's misfire was a faulty metering unit, and starting needed thought: "Full-choke and a whiff of throttle does the trick when cold", he wrote, and full choke again after half an hour standing warm. Aaron Severson, of Ate Up With Motor, adds that the injected engine was known for a rough idle, and TR-Register Deutschland that the three throttle spindles wear and let in air.

Set up properly, it worked. After Triumph's engineers rebuilt the system on Richardson's car, he covered 25,700 km (16,000 miles) without trouble from it, and he wrote:

Practical Classics suggests fitting a Bosch pump in place of the Lucas one, and checking the injectors, metering unit and pressure regulator and replacing any that need it.⁠source 1​source 3​source 9​source 10​source 11​source 12​source 13​source 14

Every power figure for the TR6 belongs to a rating, and the ratings are not all on the same basis. Triumph's figure for the first injected engine, in the 1970 brochure, names no standard. Later British brochures gave a lower figure for the same engine, and the German registration papers one in metric horsepower to the DIN standard. When the CR arrived, Richardson summed the figures up:

The TR Register adds that the CR's figure was "measured to different standards" from the CP's, and so "not as big a de-tune as it looked", without saying which standards; Ate Up With Motor and Revington TR give the CR a figure a point lower, which Severson calls net and DIN, and TR-Register Deutschland a DIN figure lower still.

The American ratings are clearer. The launch figure of 1969 was printed with no standard, though Severson calls it net. The importer's specification for the 1972 model year gave a slightly higher figure rated to the SAE standard, with lower compression, and the January 1973 announcement called it SAE net; the same 1972 table had a second, higher row with no standard named. The specifications give each figure with its rating and source.

The American engine changed almost every year. In 1969 its two Strombergs already had smog controls, with a heated inlet manifold and a valve for positive crankcase ventilation. A new inlet manifold followed for the 1970 model year, and for the 1972 model year lower compression, which the importer said cost no power, and an exhaust with twin downpipes. The 1973 cars gained a valve to stop the engine running on after it was switched off.

By the 1974 model year, the importer's newsletter listed a closed crankcase; exhaust-gas recirculation, worked by a vacuum valve at higher road speeds, to cut oxides of nitrogen; evaporative-loss control, with a sealed filler cap and a carbon canister ahead of the engine; a thermostatic vacuum switch and vacuum retard at idle; and Strombergs with throttle by-pass valves and temperature compensators. The canister was to be renewed and the recirculation checked every 19,300 km (12,000 miles). Air injection followed for the 1975 model year. Even the cars for the 49 states outside California, Severson writes, "became increasingly festooned with emissions-control devices"; the US TR6 page explains the cars for California.⁠source 5​source 19​source 17​source 18​source 20​source 14