Turbocharged diesels with two-piece pistons
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• A range of Detroit Diesel turbocharged two-stroke diesel engines with output ratings up to 350 bhp, announced by General Motors Ltd. features two-piece cross-head pistons_ It is claimed that the pistons enable outputs to be increased by turbocharging without reducing engine life.
The new range comprises the 6V-71T V6. the 6-7 IT in-line six and the 8V-71T V8 models. Both the 6V-71T and 6-71T are available in ratings of 250 bhp and 262 bhp. while the 8V-71T has ratings of 308 bhp, 335 bhp and 350 bhp. Turhocharging gives an increase in output of around 15 per cent compared with the powers that would be produced by the engines in naturally aspirated form.
A lower section of the cross-head piston carries the skirt and accommodates the thrust forces of the connecting rod. Separation from the crown section eliminates high thermal loading and loading by combustion pressure_ The piston operates virtually without distortion of the skirt and the crown section "floats" in a central position throughout the circle. While the compression rings are located in the crown section, the skirt section carries the oil-control rings. Joining the two sections, the gudgeon pin has a load area that is centred over the connecting rod and this reduces pin bending stresses to a minimum. Eight load-carrying struts of the crown section also function as cooling tins. Both sections are made of malleable iron.
Features of the standard range of Detroit Diesel engines that were recently introduced by GM. and are incorporated in the new series.. include a redesigned cylinder block which reduces the temperature of the lower part of the cylinder liner and of the piston skirt. A throttle delay device obviates "smoke puffwhen the engine is accelerated, and a type of injector is employed that is designed to reduce smoke emission_ The series complies with current Federal exhaust emission standards in the USA.