The Cummins V555 saves 6001b
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BASED on an engine developing 240 bhp at 3300 rpm, a Cummins oversquare V8 diesel new to Britain is derated to 225 bhp at 3000 rpm to give a longer life and improve durability. It has a longer stroke than the V-504 21013hp unk.
Developing 225 bhp (BS AU 141a: 1971 gross) at 3000 rpm, the Cummins V-555 V8 diesel has a dry weight of 1710 lb which represents a saving of some 600 lb compared with Cummins' best-selling engine, the 220 bhp NH-220 unit. Originally rated at 340 bhp at 33.00 rpm and tested at outputs up to 360 bhp, the V-555 was derated by reducing the rpm to give a longer life and improved reliability.
Improved features of the engine include a redesigned combustion chamber, steel-backed big-end bearings of increased diameter, tapered little-end bearings and cam-ground aluminium pistons with three rings. In common with other engines in the Cummins range, the V-555 has fourvalve cylinder heads and PT injectors. An induction-hardened crankshaft provides for regrinding the big-end and main journals, while the oil pump is a• self-contained subassembly that is readily accessible after the sump has been removed.
Of oversquare design, the unit has a bore of 117.5mm (4-kin) and a stroke of 104.8mm (4I-in) and it develops its maximum torque of 4451b ft at 1800 rpm, the capacity of the unit being 9.1 litres. Maximum piston speed is 2060 ft /min and the rated bmep is 107 psi. A minimum specific fuel consumption of 0.371b/bhp/hr is obtained at 1900 rpm and the consumption curve is virtually flat between 1700 rpm and 2200 rpm. The compression ratio is 17 to 1.
Longer liners
The bore /stroke ratio of the V-555 is 0.892, the ratio of the Cummins 504 V8 210 diesel being about 0.81, which represents a small but significant increase in the relative length of stroke. While the cast-iron wet liners of both units are centrifugally cast, the liners of the V-555 are 1.5in longer than those of the V-504 and the pistons have a corrrespondingly greater depth. Crankpin diameter has been increased from 2.5 in to 2.75in.
The cam-turned piston skirt has a ;mooth finish and a slight taper below he ring belt, the metal being relieved n the gudgeon-pin area to reduce 'eciprocating weight. Made of ductile ron, the top compression ring is of he chrome-plated barrel-faced grooved-back keystone type, the kecond compression ring being of the :hrome-plated cast-iron taper-faced grooved-backed rectangular type. The Dil-Control ring is also of ductile iron, is backed by a coil-type steel expander and is chrome-plated on its inner face as well as the outside to reduce friction between the ring and the expander.
Following the example of the V-504 the pistons of the V-555 have crowns without valve pockets and this is conducive to effective swirl control, the elimination of pockets having been made possible by the use of a camshaft providing minimum valve overlap consistent with good volumetric efficiency. A contoured swirl plate under each of the two inlet-valve seats promotes the necessary air swirl in the combustion chamber, which has a diameter of 3.15in. Peak cylinder pressure of both engines is 1300 psi, but heat rejection to the cooling water is substantially lower in the case of the V-555.
Special attention has been given to cooling, the water flow being equally divided between the two cylinder blocks controlled by a single modulating by-pass thermostat located at the front of the engine on the right
The water circulates from ' the outside of each bank around each cylinder to the head with a flow rate of about 80gal /min. An oil cooler of the bundled-tube type is connected in parallel with the cooling system.