Experimental Rolls-Royce engines

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Normally no information reaches the historian about experimental Rolls-Royce engines, so it was with great interest that I read the excellent address, “The History of a Dimension,” by S. H. Grylls, M.A., Chief Engineer, Motor Car Division, Rolls-Royce Ltd., delivered to the Automobile Division of the I.M.E. last month, for, although this is intended as a very erudite exposition on the manner in which for 40 years fuels, lubricants and metallurgy have kept pace with m.e.p.’s and rev./min., only Young’s modulus resisting change, there are fascinating references to experimental R.-R. power units.

Mr. Grylls tells us, for instance, that when Royce decided on a small R.-R. in 1919, he designed a twin o.h.c. engine which was completed by 1920. This 3 in. x 4 1/2 in., 20.6 R.A.C. h.p. engine gave 53 b.h.p. at 3,000 r.p.m. and weighed 650 lb. with all components. It was known as the “Goshawk I” or IG1, and was driving a chassis bump-rig at the factory in 1931. The simpler push-rod 6-cylinder was adopted for production. Noise from flywheel resonance at 3,100 r.p.m. and disintegration of distributor and timing gears at just below 3,300 r.p.m. (or 76 m.p.h. in the test chassis) were early difficulties with this 20-h.p. Rolls-Royce, but its white metal bearings lasted for some 9,000 miles at full-throttle on French roads. The paper contains most interesting details of how this engine was developed and of how R.-R. and Packard employed different methods to overcome crankshaft vibration problems—Fast & Late should publish in full! By 1933 a nitrided crankshaft gave 30,000 miles’ bearing life.

When the Bentley Co. was acquired a 2,360-c.c. blown engine (the “Peregrine”) was experimented with before the J1 engine was accepted for the first 3 1/2-litre Bentley, this differing from the 20/25 R.-R. engine in respect of head, camshaft, cr. and the use of twin S.U. carburetters. The simple solution is described which cured big-end failure in this engine—run light on the test bed the life of 160 hours fell to 15 sec.! An o.h.c. version of this engine gave 160 b.h.p. on open exhaust and a centrifugally supercharged push-rod engine was also built but the increase in m.e.p. occurred too high in the rev, range to interest R.-R. Another experimental engine was the 3.4 in. x 5 in., 4,404 c.c. J3, but its critical speed was so low that even high axle ratios were of no avail.

Development of the 25/30 “Wraith” engine is discussed in detail, and the experimental 1938 i.o.e. 6-cylinder and 4- and 8-cylinder engines is referred to. These engines had a life of at least 100,000 miles without inspection, on French roads. It is confirmed that only a dozen straight-8 Phantom IV Rolls-Royces were made. By 1959 the 6-cylinder F head car engine, with inlet valves 2.150 in. in dia., was developing 178 b.h.p. and 135 maximum m.e.p.

The military straight-8 B81 R.-R. engine was required to run non-stop at full power for 168 hours, on fuel containing 3.6 c.c. lead per gallon. On lead-free fuel 706 hours were possible. This engine, with 8-port head and large dual d.d. carburetter, gave at least 235 b.h.p. The West German Army wanted it for use underwater and insisted on 100 hours at full power with the coolant outlet at 100C. unpressurised. 22,000 hours of development running on test-beds was needed before the Bundeswehr got what it wanted!

A 6-cylinder R.-R. engine gave 205 h.p. with a 10-to-1 c.r. on 100-octane petrol, and 215 h.p. with fuel injection, and the 8-cylinder reached 275 h.p. with fuel injection, and 268 h.p. with triple S.U.s on 80-octane fuel. All had 4.150 in. cylinder centres and 4 1/2 in. stroke. Intriguing details of how a reliable tick-over with twin carburetters was obtained is included.

In 1947 an 8-cylinder B-range engine was cast in aluminium, with 3 3/4 in. bore dry-liners and three carburetters and run for some years in a long-nosed Bentley, and one of a batch of six B60 3 1/2-in. bore 6-cylinder light-alloy engines ordered by the War Office but abandoned, also found its way into an experimental car. This extremely interesting paper concludes with details of other experimental light-alloy engines, leading to the present Rolls-Royce V8 production power unit.—W. B.

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