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).
Performance trials comparing different vehicle configurations, focusing on top speed and acceleration.
| Identifier | ExFiles\Box 29\3\ Scan325 | |
| Date | 23th June 1931 | |
| - 2 - The most interesting point is that with the C.O. open 16.G.IV. is only 1 M.P.H. slower than 18.G.IV. whereas with the C.O. closed this difference is increased to 3.9 M.P.H.- i.e. we can get an appreciable increase in speed by reducing our back pressure in the present 25 HP. exhaust system. The max. lap speed for 16.G.IV. was exceedingly good, considering that the conditions were very unfavourable to high speeds owing to a big head wind down the straight. We were disappointed with the max. speed of 18.G.IV. considering that we had 14 B.H.P. more than 16.G.IV. It is difficult to allow for the windage of the two bodies however. With a China unit, C.O. closed, 18.G.IV. could only lap at 61.4 M.P.H. so that we have further evidence that the body of this car is not good for high speeds. The standard car was 5.4 M.P.H. slower than 18.G.IV. The trials was very smooth; both 18.G.IV & 16.G.IV. were rough at maximum speeds and we shall try the W.W. tail bearing as soon as possible to see if it eliminates this vibration. ACCELERATION TESTS. Though 18.G.IV. weighed 2 cwts. more than G.S.R.14 and nearly 4 cwts. more than 16.G.IV. it was possible to obtain an approximate relative performance by ballasting with passengers. The acceleration of 18.G.IV. was definitely superior to the trials car between 10 & 60 M.P.H. The difference between 18.G.IV. and 16.G.IV. was not so marked, but between 20 & 30 M.P.H. 18.G.IV. had the advantage. SUMMARY. The tests show the advantage of the Japan head, of a free exhaust system, and of the 'ramming' induction pipe for acceleration for which purpose the existing P.II. twin carbs. were designed. We apparently require 80 B.H.P. to give a standard maximum bodied 25 HP. car, a genuine top speed of 70 M.P.H. It would be interesting to try the same unit in a Continental type 25 HP. and see how the performance compares with that of our competitors. Our other problem is to try and make 18.G.IV. | ||