This 141 bhp unit should be long-lived and economical
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by P. A. C. BROCKINGTON, MIMeehE
THE case for the turbocharged engine is given a big fillip by to-day's announcement by the Ford Motor Co. Ltd. of a turbocharged version of its 360 Cu. in. diesel engine. It is particularly significant that the unit—called the Turbo 360—is fitted as original equipment, as distinct from an option, in a range of goods chassis (the new 20-ton-gross tandem-axle six-wheel series) that will be produced in quantity.
While the Turbo 360 has a useful role as a power-output gap-filler in the units produced or used by Ford, its inclusion in the Ford range is fully justified on merit alone. Its claimed life (100,000 miles) is equivalent to that of the basic naturally-aspirated unit and it is reported to be more efficient and economical. Moreover, the weight penalty of providing an increase in power of 25 per cent is only 491b.
Of particular importance as a favourable "compatability factor", the turbocharger also has a rated life of 100,000 miles. Many of the changes made to the 360 Cu. in. engine to suit turbocharging have been applied to the basic engine as a production economy.
While the Ford 360 cu. in. naturally-aspirated diesel has an output of 113 bhp net (128 bhp gross) at 2,800 rpm, the Turbo 360 produces 141.5 bhp net (150 bhp gross) at the relatively slow speed of 2,400 rpm— which should reassure the typical operator about its wearing properties. The DIN rating is 143 bhp at 2,400 rpm.
Bore and stroke of the unit (4.125in. and 4.524in. respectively) are unchanged and peak torque of the Turbo 360 is 338 lb. ft. net at 1,700 rpm which compares with a net torque of 262 lb. ft. at 1,500 rpm produced by the non-blown engine. Gross
torque outputs of the two units are respectively 349 lb. ft. at 1,800 rpm and 276.5 lb. ft. at 1,600 rpm.
The thermal efficiency of the basic engine is increased from 34.5 per cent to 38 per cent by turbocharging, which corresponds to a reduction in specific fuel consumption from 0.38 lb /bhp /h to 0.37 lb /bhp /h. Ford says that a number of Turbo 360s fitted to the tractive units of 18-ton-gross artics are returning a consumption of 13 mpg and it is pointed out that turbocharging gives "much cleaner exhaust characteristics", reduces combustion and exhaust noise and produces a smoother drive.
The turbocharger employed is a Ho!set 3LD-9 1.14 unit. It weighs only 19.75Ib and provides a pressure ratio of 2 to 1, running up to 90,000 rpm to deliver 350 Cu. ft of air per minute. Turbocharging increases the volumetric efficiency of the engine from 83 per cent (of the naturally-aspirated diesel) to an equivalent of 132 per cent. The compression ratio has been reduced from 16.5 to I to 15.7 to 1 to cater for turbocharging.
While the Turbo 360 is dimensionally similar to the naturally-aspirated unit, it has been considerably modified structurally. The crankshaft of the new engine is forged from EN 19S steel having a higher tensile strength than the EN 18R steel of the naturally aspirated unit's crankshaft. A heavier Metalastik vibration damper is used and crankcase bulkheads have been strengthened to accommodate the increased loading.
Aluminium-tin main and big-end bearings are still used and the journals are the same size, but more substantial main-bearing caps are employed to cater for the higher loads.
Completely re-designed, the pistons of the Turbo 360 are stronger and have better heat flow. The "gothic-arch" structure adopted improves heat flow from the crown to the ring belt area—there is more metal behind the rings. Good heat dissipation is of particular importance because turbochar ging raises the peak temperature of the crown from 300 degrees C to as much as 325. At the same time peak pressure is increased from 1,200 p.s.i. to 1,600 p.s.i. and the b.m.e.p. is improved from 113 p.s.i. to 146 p.s.i. which represents a gain of 29 per cent.
Also of heat-flow interest, the pistons are profiled in a special way to aid heat dissipation by improving the contact characteristics of the piston surfaces and bore. The skirt is designed to improve the heat drain from the two lower lands to the water jacket and thermal stressing of the pistons has been further reduced by chamfering the top edge of the combustion chamber bowl and by contouring the valve recesses.
As before, the pistons are of the barrelled-tapered-oval type and are made of BS 1490 aluminium alloy. As with the unblown engine, the three compression rings and single oil-control ring are above the gudgeon pin. All the compression rings are chromium-plated and the width of the land between the first and second rings has been increased to give better support of the highly loaded top ring. To cut ring wear, the first two compression rings are mounted in a cast-iron insert.
The inlet valves as well as the exhaust valves of the Turbo 360 are of the two-piece type, having heads of 2I-4-N steel and stems of EN 18C material. Both valves now have seat inserts designed to prevent thermal cracking between the ports.
A strengthened casting is used for the cylinder head, and holding-down bolts of improved material enable a higher tightening torque to be applied. This aids gasket sealing, which is further enhanced by using a special gasket developed for the engine. The gasket is of steel-wire combined with asbestos and is reinforced with double-thickness aluminium-plated steel rings round the cylinder bores. The surfaces are treated to provide special friction properties. Oil-pump delivery has been increased from 8 gal /min to 8.4 gal /min and a Series III oil is specified to cater for the higher combustion temperatures and to aid dispersal of carbon.
The required increase in injection-nozzle capacity has been provided by increasing the diameter of the four holes from 0.29mm to 0.33mm. And the cracking pressures of the needles have been raised from 175 atmospheres to 195 atmospheres. Adequate fuel delivery of the Simms Minimec pump has been ensured by increasing the diameter of the elements from 8mm to 9mm, while detail modifications have been made to the pump to enhance its load capacity. Two Simms paper-element filters are fitted to the turbocharged engine to accommodate the greater flow of fuel.
In contrast to the constant fuel delivery rate of the naturally aspirated engine, the delivery rate of the pump of the Turbo 360 rises from idling speed up to about 1,600 rpm to match the output of the turbocharger. This is of importance operationally because it enables the system to be tailored to give a good low-speed torque.
The exhaust manifold comprises two iron castings and is above the inlet manifold. A novel type of light-alloy intake manifold receives air from a Cyclopac paper-element air cleaner, conveys the air to the compressor of the blower and receives air from the compressor to distribute it to the cylinders. This gives a very neat installation and reduces heating of the intake air to a minimum.
. Features developed for the Turbo 360 that have been incorporated in the naturally-aspirated engine include the modified cylinder block, crankcase and cylinder-head casting, bore finish, cylinder head bolts and fuel-injection pump.