Triumph TR4 - Engineering

Engineering

The pushrod 4-cylinder engine based on the early design of the Ferguson tractor engine, was continued from the earlier TR2/3 models, however the displacement was increased from 1991 cc to 2138 cc in the TR4 by increasing bore size. Gradual improvements in the manifolds and cylinder head allowed for some improvements culminating in the TR4A model. The 1991 cc engine became a no-cost option for those cars destined to race in the under-two-litre classes of the day. Some cars were fitted with vane-type superchargers, as the three main bearing engine was liable to crankshaft failure if revved beyond 6,500 rpm. Superchargers allowed a TR4 to produce much more horse-power and torque at relatively modest revolutions. The standard engine produced 105 bhp (78 kW) SAE but, supercharged and otherwise performance-tuned, a 2.2-litre I4 version could produce in excess of 200 bhp (150 kW) at the flywheel. The TR4, in common with its predecessors, was fitted with a wet-sleeve engine, so that for competition use the engine's cubic capacity could be changed by swapping the cylinder liners and pistons, allowing a competitor to race under different capacity rules (i.e., below or above 2 litres for example).Standard inline-four engine

Other key improvements over the TR3 included a wider track front and rear, slightly larger standard engine displacement, full synchromesh on all forward gears, and rack and pinion steering. In addition, the optional Laycock de Normanville electrically operated overdrive Laycock Overdrive could now be selected for 2nd and 3rd gear as well as 4th, effectively providing the TR4 with a seven-speed manual close ratio gearbox.

TR4 were originally fitted with 15x4.5" disc wheels. Optional 48-lace wire wheels could be ordered painted the same colour as the car's bodywork (rare), stove-enamelled (matte silver with chrome spinners, most common) or in matte or polished chrome finishes (originally rare, but now more commonly fitted). The most typical tyre originally fitted was 155x15 bias ply. In the US at one point, American Racing alloy (magnesium and aluminium) wheels were offered as an option, in 15x5.5" or 15x6" size. Tyres were a problem for original owners who opted for 60-spoke wire wheels, as the correct size radial ply tyre for the factory rims was 155x15, an odd-sized tyre at the time that was only available from Michelin at considerable expense. The much more common 185x15 radials were too wide to be fitted safely. As a result, many owners had new and wider rims fitted and their wheels re-laced.