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).
Test report comparing cooling performance between cars with louvered and plain bonnets to address overheating at high speeds.
| Identifier | WestWitteringFiles\T\2January1929-June1929\ Scan249 | |
| Date | 12th September 1927 | |
| contd :- -2- Our tests shew that the SS.{S. Smith} is better cooled for hill climbing than any 40/50 HP. car we have previously had. We know that the specific complaint was that the car over-heated at high speeds. We have repeatedly proved that high speed cooling is a matter of bonnet ventilation. In our last test on Brooklands (Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}2/LG12.9.27) we showed that a car fitted with a louvred bonnet and driven at max. speeds would have a radiator temp. 20°C below that of the car driven in a similar manner with a plain bonnet. In view of this enormous difference we do not anticipate that we shall ever be able to build a car which can be driven at max. speeds in hot weather without over-heating if a plain bonnet is fitted. On the other hand it is a fact that the present standard Phantom has given a reasonable satisfaction without louvred bonnets. We therefore carried out a high speed test comparing a standard chassis on test fitted with a covered body with SS.{S. Smith} car 19-EX which was the car of which PN.{Mr Northey} specifically complained. Both cars were fitted with the equivalent of 14 tooth axles. The cars were driven as hard as possible over a 15 miles stretch of road averaging about 50 m.p.h. Both cars had unventilated bonnets. The ats. temp. was 23°C which is of course a summer temp-erature. (We have frequently had days with a temp. of 30°C on our 10,000 miles tests.) There was a light wind which made a considerable difference in the two directions. Against the wind the max. temperatures attained were : SS.{S. Smith} car 19-EX.............. 75°C. Phantom car 73-OR............ 85°C. contd :- | ||