From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Analysis of engine performance focusing on exhaust valving and comparing Bentley and Kestrel Ramp head designs.
| Identifier | ExFiles\Box 134\2\ scan0038 | |
| Date | 30th May 1935 | |
| -3- The losses due to such edges increase rapidly at high velocities and charge densities, and we propose to try a modification which will eliminate such edges on our own ports. A Ramp Head with inlet valve area increased to give a ratio to piston area of .212 is at present awaiting test. The effect of the internal shape of the head may have some effect and we shall soon get a value for this as there is already in hand a Merlin 'D' Penthouse Head for the Aero Universal Unit, which can be compared with the existing Ramp head. (c) Exhaust Valving. The ratio of exhaust area to piston area is .1425 on the Kestrel Ramp and .167 on the Pegasus. A comparison at 3000 ft/min. piston speeds shows that the Pegasus is 9.5% better naturally aspirated and 12.5% better with 8" boost. This rather suggests that the smaller exhaust area may be offering a restriction under boosted conditions, particularly as the duration of exhaust opening is also shorter on the Kestrel Ramp. A Ramp head in which provision has been made for increasing the exhaust area is awaiting test. (2) Bentley High Power Two Inlet Valve Head and Kestrel Ramp. As the friction losses due to increased piston friction on the car single cylinder units is very much larger than on the aero units the only fair comparison is between I.M.E.Ps. It should be noted that the relative valve area which can be obtained on the high power head is much greater than that which it is possible to get on either a sleeve valve engine or a four-valve overhead camshaft engine although it should be appreciated that the high power head is in cast iron and thus is not handicapped by valve seat inserts which cut down the inlet area available on an aluminium head. The main reason for including the high power head in these tables is that it shows very clearly that the greater the inlet valve area, the higher the m.e.p. at the top speeds for naturally aspirated, and the less boost required for a supercharged engine for a given m.e.p. The limit to increased inlet valve area will occur when the peak of the m.e.p. curve occurs at the maximum speed of the engine, a condition which is not even reached by the high power head. Contd: | ||