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).
Comparative table of radiator tube performance based on critical air temperature tests.
| Identifier | ExFiles\Box 16\2\ Scan009 | |
| Date | 21th April 1931 guessed | |
| TYPE OF RADIATOR TUBE CRITICAL AIR. TEMP oC The difference between the top water temp. and Ats (st) subtracted from 100oC. This temp. represents that at which the car will eventually boil in still air if driven sufficiently long full throttle | TYPE OF RADIATOR TUBE | 60 MPH. No bonnet ventilation. | All Out No bonnet vent. | All Out Vertical bonnet louvres | |---|---|---|---| | Small Hexagonal Ended American Tube Hexagon .325 across Flats Centre .255 Dia. round. No. of Dents 18. | 44.5, 46. | 38.5, 38. | 45.5, 46. (Partial Shutters 41.5) | | Large Hexagonal Ended American Tube. Hexagon .360 Across Flats Centre .300 Dia. round No. of Dents. 20. | 40, 41.5 | 32.5, 36 (This reading requires confirmation) | 41.0, 42.5 | | Present standard tube. 6/7½ mm. Round E.79446. 4 dents/tube | 39.5 | 31. | 38.5 | | Square tube E.81389. 6 mm. square centre Ends expanded to 7½ mm. horizontally only. i.e. 1½ mm. vertical waterways. no horizontal waterways. | 38. | 39.5 | 39.0 | Tests on 13-EX. Brooklands. Car weight 48 cwt. Axle 11X41. All radiator dimensions 25.9 X 23.7. | ||