Cummins-powered Eight-wheeler is Fast
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1AS1 acceleration and hill-climbing are
not normal characteristics of British ;ht-wheelers, the tendency being to ploy slightly less power than is desirIle, in the interests of fuel economy. te Seddon DD8/1-1F-6, powered by the immins HF-6 179 b.h.p. oil engine, wever, shows what can be done with 'chicle of this size when a high-powered gine is installed.
Tests made last week showed that 30 m.p.h. could be reached from standstill in 32.8 seconds, which is a figure more normally obtained from vehicles in the 7-ton-payload range, whilst, because of its gearing, the eight-wheeler has a maximum speed of about 45 m.p.h. The rearaxle ratio is 5.6 to 1.
Severe fog in the Manchester area made it impossible to conduct a fuel-consumption test, but Cummins engines are known to be economical (the Seddon Sirdar six-wheeler running at over 30 tons gross gave 9.15 m.p.g. when tested last year), so a fuel figure of at least 9 m.p.g might be expected.
The Cummins HF-6 is a six-cylindered 11-litre engine and by British standards its governed speed is high for an engine of this size-2,100 r.p.m. Its maximum torque, 500 lb.-ft., is developed at 1,350 r.p.m. and an 18-in.-diameter single-dryplate clutch with air-pressure assistance, is employed.
A David Brown 561 five-speed constantmesh gearbox with a torque capacity of 750 lb.-ft. is mated to the Cummins engine in the Seddon application. Its forward ratios are 8.94, 5.18, 3.1, 1.705 and 1 to I, whilst reverse is 9.25 to I. Chassis weight with this engine and gearbox is about 9 cwt. greater than with a Gardner engine, and the kerb weight of the vehicle as tested was about 71 tons, its gross weight being 241 tons.
Superlative hill-climbing was demonstrated when an ascent of a 13-mile 1-in12 gradient was made in a total time of 8 minutes 55 seconds, the lowest speed in second gear being 7 m.p.h. It was also possible to restart on a 1-in-61 slope in second gear. As might be expected of an engine of this output, it is rather more noisy than less-powerful British engines and the exhaust tends to be raucous.