Tailored engines from Cummins
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—and powers up to 420 bhp
• "Tailoredrather than "new" was how Mr J. A. Gray, managing director of Cummins Engine Co Ltd, described a revised range of Cummins engines announced last week.
Changes which have been "tailored" for the NH in-line six-cylinder units are of two kinds—a repositioning of components, and modifications to suit the probable needs of the Construction and Use Regulations for goods vehicles for the 1970s.
Ever since Cummins engines in the NH range were first built at the Shotts, Scotland, factory they have been virtually to the American parent company design and a number of the components have not been positioned suitably for use with righthand-drive vehicles. Now these fittings" have been relocated so that they do not interfere with right-hand-drive steering boxes, brake linkages and pedal operation.
With the advent in mind of stricter noise and smoke regulations, as well as the likelihood of a bhp per ton requirement before long, changes to performance characteristics have been made which provide ade quate power ranging from 205 bhp up to 335 bhp now and shortly up to 420 bhp—while still retaining the qualifications needed to clear the BSAU/141 engine test standards.
Replacing completely the old familiar models NH 180, 200, 220 and 250, the new range is in two groups, one of which consists of the normally aspirated NHK 205 and 230 models and the other four turbocharged NTK units.
The smallest engine, the NIIK 205, has a 5.125in. diameter bore and a 6in. stroke. The other five engines all have the 6m. stroke but a 5.5in. bore.
Outputs from the four higher powered engines range from 252 bhp to 335 bhp but the smallest is specially tuned as a high torque unit, producing its maximum torque of 850 lb.ft. at 1200 rpm, which is approximately 500 rpm lower than the speed at which the other engines produce peak torque. Because of its special tuning this engine has the letters HT (high torque) suffixed to its designation. that is NTK 252 HT. The NTK 270 engine has a peak torque of 755 lb.ft. at 1550 rpm; the 310, 860. lb.ft. at 1600 rpm; and the 335, 938 lb.ft. at 1600 rpm. The figures in all these designations indicate the bhp produced.
All the turbocharged engines may have the turbocharger mounted in one of three alternative positions, allowing designers plenty of scope for air intake and filter layout.
To combat noise emission much work has been carried out by Cummins. To overcome the problem with current engines the firm is experimenting with panelling the sides of the engine block with sound absorbent material. All the units produced at Shotts will easily satisfy the type approval requirements of the new British Standard but in order to build quietness into future designs a considerable amount of research has been done on blocks, heads, sumps and valve rocker covers by Cummins engineers both in the United States and at Essen, West Germany and a study has been made for the company by a Southampton University professor.
When the latest engines were introduced to the Press last week brief reference was made to a new reconditioned-unit service which is to be put in operation shortly, and extensive premises are being constructed to house this activity.