Vew Rolls-Royce Engines With Four-Valve Heads
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1E1NG shown for the first time at ?the Public Works Exhibition (which
petted on Mondays by Rolls-Royce,
td., Oil Engine Division, Shrewsbury, le company's new -Mk. 4 range of
igines' is based on the existing crankiSe assemblies of standard C-range nits, but incorporate a number of rigimil features, including .four-valVe /finder heads. A-. separate head ,is, fitted to each ■ linder,.-and is employed in conjunction
ith a fuel-injector of improved designid a modified piston. Initially available. sixand eight-cylindered turbocharged >rm., Mk:. 4 Units Will be offered to ierators requiring greater Outputs than lose afforded by the standard types of -Series 'engine.
Naturally aspirated and supercharged Xand eight-!cylindered engines will ter he Included in the range, in addition a four-c;ylindered unit in. naturally. ;pirated, supercharged and turbocharged
alp. It. is emphasized by the, company, the" types of 'standard' component.. Tiduced have not been increased, aOart om the. parts mentioned.' Equipped with a dynamic balancer, the rbocharged version of the C4 four
lindered engine also made its first
>-pearance at the Exhibition. Formerly e range of four-cylindered units was stricted to naturally aspirated and Lpercharged engines. Of the contratating type, the balancer is gear-driven orn the front of the crankshaft.
The Mk, 4 six-cylindered turbocharged [gine has a maximum automotive rating 335 b.h.p. at 2,100 r,p.m., which reprents an increase of 11+ per cent. corn
a-ed with the output of the standard range engine of 300 b.h.p. at the same eed. The maximum torque is improved am 850 lb. ft. at 1,300' r.p.m. to 6 lb. U. at 1,600 r.p.m. In the case of the eight-cylindered rbocharged engine, a higher gain in
tput is obtained, the maximum b.h.p.
2,100 r.p.m. being raised from 400 to 0, an increase of 121 per cent., whilst maximum torque is raised from [35 lb. ft. at 1.400 r.p.m. to 1,198 lb. ft. 1,600 r.p.m. The rating of naturally pirated engines is increased by about
ien per cent.
Mk. 4 units also show to advantage th regard to specific fuel consumption. ! minimum consumption of the six cylindered turbocharged .engine being redueed from 0352 lb/b.h.p.--hr. at 1,400 r.p.m. to 0.347lb./b.h.p.-br, • at 1,800 r.p.m. The consumptidn of the Mk. 4 eight7eyliTidered engine is -0:357 lb fia,h.p.hr. at 1,800 r.p.m., compared with a minimum consumption of 0.362 lb./b.h.p.hr. at 1,400 r.p.m. of the standard C-type. Turbocharging increases the maximum rated output of the four-cylindered engine at 2.100 r.p.m. from 140 b.h.p. to 200 b.h.p. In supercharged form the engine produces 182 b.h.p. at the same speed. The use of individual cylinder-heads gives more uniform load distribution of the set screws and improves 'gasket sealing at higher cylinder pressures. Greater reliability at higher outputi-is afforded by the four-valve head, as well as improved breathing. A favourable heat-dissipation area is provided by the relatively small exhaust valves, and they offer greater resistance to flexing when opened against a high cylinder pressure. Port diameter of the two inlet. valves is 11 in.. whilst each of the exhaust valves
has a port diameter of 1,i in. The diameter of each valve of the two-valve head is approximately 2 in.
A single push-rod and tappet is employed to operate each of the two .sets of valves, a bridge piece being used having a centre section which acts as a thrust pad. The camshaft is of the standard type in every case. Single valve springs are fitted. Apart frpm improving port characteristics in. the vicinity of. the combustion space, the design of the four-valve head gives better cylinder filling by virtue of the .shape and contour of the inlet passages. .Siamesed ports are avoided by joining the pasSage$ of "adjaCent cylinders close . to the outer :port of the cylinder head The shape of the passages improves filling, and tangential entry of the air promotes swirl iq. the. , combustion chamber without creating wasteful turbo' knee on the port-side of the valves.
Location of the four-hole injector has been changed; so that its axis is vertical in the cylinder instead of being at an angle, and a modified spray pattern is employed. ,• Following , normal practice; the combustion ,chamber is of the slraight-sided toroidal tYpe, but dimensional modifications. • have , been, applied to .match the chataeteristie§ of the head. Connections to the injector..spill -system are arranged -externally to the cylinder to obviate dilution of the lubricating oil. Sixand eight-cylindered engines are equipped with the new C.A.V. high. capacity B.B. type of injector pump. Supplied by the Wellworthy company, the pistons are of the Alfin ring-insert type; a W.63 light alloy is used, and this material affords a high resistance to cracking round the toroidal cavity.