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).
Letter detailing test results on exhaust systems and camshaft timings for a 4¼-litre Bentley engine.
| Identifier | ExFiles\Box 134\1\ scan0091 | |
| Date | 15th June 1938 | |
| 223 Experimental Dept. Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}/MH.{M. Huckerby} 15th. June 1938. Dr. J.C.Morrison, James Watt Engineering Laboratories, The University, GLASGOW. Dear Sir, I have been instructed by Mr. Robotham to give you some data regarding our latest tests on exhaust systems, in reply to your letter of the 13th. Our normal 4¼-litre Bentley has a 3 port exhaust system, the 2 cylinders per port being siamesed and with the standard single system of which construction you are familiar, there is a drop of 13.5% to the open exhaust figure and a back pressure in the manifold of 9" Hg at peak power R.P.M. Using the same common 3 port manifold but with a double outlet and 2 standard exhaust systems, separate from the manifold onwards the power loss to open exhaust is reduced to 5% and the back pressure registered at 4 - 5 INS Hg. The siamesed 3 exhaust port head cannot, of course, be separated into a twin manifold and in view of the good results obtained with the common manifold with duplex systems we wonder what advantage we would be likely to gain with a 4 port or a 6 port head which can be separated in the manifold, both in respect of power and silence. Regarding camshaft timings and power output, we recently tried a timing as follows:- Inlet Open 3° After TDC. EO 36° Before BDC. Inlet Closes 46° After BDC. EC 2° After TDC. in comparison with 6° earlier that is Inlet Open 3° Before TDC. EO 42° Before BDC. Inlet closes 40° After BDC. EC 4° Before TDC. The above later timing showed an appreciable increase in high speed power with no loss of MEP at the low speeds. we have | ||