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).
Technical description of an 8-cylinder Bugatti engine, detailing general specifications, valve timing, and crank arrangement.
| Identifier | Morton\M16\ img008 | |
| Date | 2nd June 1930 | |
| E.{Mr Elliott - Chief Engineer} C..Hs.{Lord Ernest Hives - Chair} X2266 Rg{Mr Rowledge}/Tsnl/ME.2.6.30. Re: 8 CYLINDER BUGATTI ENGINE. ----------------------------- Mr. Jenner asked me to send on prints of the crankshaft etc., of my car, since you are now interested in straight eights. I thought a few remarks would also be of interest:- (1) GENERAL. The engine is 60 x 88 m.m., two litres capacity; compression ratio approximately 6 1/2/1. Considering its power and performance it is very flexible indeed. There are two inlet valves and one exhaust per cylinder. The timing is:- Inlet V.O. : T.D.C. V.C.: 20° A.B.D.C. Exhaust V.O. : 50° BBDC V.C.: 12° A.T.D.C. The exhaust valve timing is fairly "racing" but, with the ample inlet valving and ports the inlet time is very "touring". I believe this is one secret of the re-markable combination of power and flexibility, i.e., they get the power without the aid of an extreme inlet timing which would spoil the low speed performance. Top gear is 3.84/1. Petrol consumption about 18 M.P.G. (2) CRANK ARRANGEMENT. As shown in the small diagram on the larger print, this differs from that of any other straight eight. The actual firing order is 15263748. This order is at least easy to remember since the two halves fire in numerical order alternately. There are two Solex carburettors, each feeding into a two-branched induction pipe with a small water jacket, each branch feeding two cylinders via a common inlet port. This port contains four valves (2 per cylinder). The crank arrangement does not appear to help the distribution, so I think it must be chosen to facilitate the design of the built up shaft. There are five main bearings, three large double-row self-aligning Skefkos, and two intermediate roller bearings, having split outer races. Another advantage of the crank arrangement is that there are only three main bearings highly loaded | ||