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).
Induction system and carburation options for the Wraith model, referencing the 20/25 arrangement.
| Identifier | ExFiles\Box 7\4\ X 608 Carburetter-page01 | |
| Date | 26th September 1934 | |
| To E.{Mr Elliott - Chief Engineer} c. to Nor. c. to By.{R.W. Bailey - Chief Engineer} x4209 608 He/Rn{Mr Robinson}/7/KM. 26.9.34. WRAITH CARBURATION. We have been considering the various schemes of induction system which have been proposed for the Wraith. In our experience distribution is one of the most difficult things to get right on any engine and next to distribution, carburation. We spent about 6 months investigating the Peregrine distribution and it took a similar period to develop the semi-expanding Rolls-Royce carburetter. Therefore if we start with a new carburetter and a new induction system it will be one of the features that will delay the car. For this reason we are anxious that a design should be available for an induction system on the Wraith which resembles something which we have previously found to be satisfactory. Considering our past experience we think that on the whole the 20/25 arrangement is the best, where slow running and even slow pulling are of primary importance and maximum power output is a secondary consideration. This scheme is of course suited to the intake and exhaust manifolds being on the same side of the head as in the Wraith, but necessitates space being left between the two centre cylinders for the minimum restriction to the gas flow. We have an exact comparison of what we may expect in the way of engine performance from tests we have done on the 20/25. In the attached curve we took a 20/25 engine and put a Bentley head on it, the engine then gave 100 H.P. We then removed the head and put a 20/25 on it with the latest carburetter. In doing so we lowered the compression ratio from 6.5 to 5.8; we obtained 88 H.P. | ||