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).
Road and idling tests on engine performance with different vacuum line connections and vacuum tank systems.
| Identifier | ExFiles\Box 40\4\ Scan270 | |
| Date | 19th October 1927 guessed | |
| contd :- -2- to upset their even running. Nos. 4, 5 and 6 cyls. only are affected. (b) Vacuum line connected to the centre of the induction pipe. All 6 cyls. are upset in this case. The engine will not run regularly during the dumping period on Nos. 1 and 6 ; 1, 2, 5 and 6 ; or on 3 and 4 cyls. (2) ROAD TESTS. Results of tests carried out on the road appear to contradict the results obtained during 'idling' tests. The slow running is very slightly upset when the standard vacuum connection is used, misfiring taking place either once or twice on one cylinder during the dumping period. When the vacuum line is connected up to the centre of the induction pipe, no misfiring takes place but the engine is slowed down considerably by the sudden even richening of the mixture. The only reason for the difference in the effect between idling and running slowly on the road is that in the case of the road condition the rolling of the car helps the engine over the sudden 'too rich' period and as the richening up is even, nothing but a temporary slowing down of the engine is noticed; whereas when idling, the flywheel momentum only can help the engine to turn over; this is not sufficient to tide over the 'too rich' period and the engine stops. It is quite possible that the Stewart vacuum tank which utilises a permanent restriction in the suction line may allow the petrol vapour to go into the induction pipe so slowly that very sudden 'richening up' does not take place i.e. it may be restricted slightly more than our Autovac and so just escape the actual engine stopping when idling. The conclusions are that connecting the suction line to the middle of the induction pipe is beneficial if the suction line is restricted to prolong the rich period sufficiently to allow the engine to run when idling (as in the Stewart) but is detrimental where no great restriction is utilised (as in the Autovac). It is better in this latter case to introduce the rich mixture to three cylinders only, leaving three to run normally. We are aware that the Autovac automatic restriction is not as efficient in this respect as the permanent restriction in the Stewart tank. It is the greatest restriction we can make consistent with correct functioning of the contd:- | ||