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).
Technical discussion on engine performance, detonation, compression ratios, and gaskets for Bentley and Wraith models.
| Identifier | ExFiles\Box 97\1\ scan0126 | |
| Date | 22th March 1938 | |
| -2- Curve (S30) illustrates this difference and it will be seen that on the non detonating line (which is the maximum power that can be used in a chassis) the actual MEP at 6 : 1 ratio is above the 6.5 : 1 ratio by 2 lbs/sq.in. at speeds up to 1250 RPM. Above 2000 RPM, however, the higher ratio shows up and gives an increase of 3 HP at maximum power. Until such time that we can produce a condition that will give borderline detonation without having to drop power on a No.3 fuel, then it is not worth having a higher compression ratio head for the Bentley lll than for the Wraith. An interesting series of curves have been done as shown on (S28) where the clearance space between the piston top and the cylinder head has been varied yet keeping the same compression ratio of 6.25 : 1. Hitherto on development of the TT engines we have obtained more power with a reduced clearance and yet keeping the same ratio. However, by the results obtained on Bentley lll there is very little difference between a clearance of .045 and .080 and actually the larger clearance is slightly in front both in respect of non-detonating power and maximum power. Another interesting curve (S29) illustrates the comparison of fuels regarding ignition advance and detonations. At 6.5 : 1 ratio on which they were tested we are on borderline detonation (developing maximum power) with Ethyl, dropping 2 - 3 lbs/sq.in. BMEP on Shell No.1 to avoid detonations, and dropping 5 - 6 lbs/sq.in. BMEP on Red Line (No.) fuel). The latter fuel is the one that we base our limitations on compression ratio and select ignition advance. We have recently been running with .030 thick cylinder head gaskets in 'Klingerit' material in place of the normal C and A gasket which varies with supplies from .060 - .085. The former besides being cheaper, is we find a better gasket from a sealing point of view. The only disadvantage obtained was that these Klingerite washers were inclined to stick to one face or the other, however, their latest treated ones are better in this respect. It is our intention to send out the next car which goes to France fitted with this type of gasket and if successful use on all of our units. This will make Wraith lll and Bentley lll 6.19 : 1 compression ratio. We originally tried these in view of complaints on Ph.lll with C and A and quite recently it was necessary to | ||