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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 from F.M. Aspin & Co. discussing a cylinder head collaboration and engine performance metrics.

Identifier  ExFiles\Box 134\1\  scan0193
Date  5th February 1944
  
COPY.

F.M. ASPIN & CO. LTD.,
ELTON, BURY, LANCS.

FMA/PC
5th February, 1944.

CONFIDENTIAL.

W.A. Robotham, Esq.,
Messrs. Rolls-Royce Ltd.,
DERBY.

Dear Mr. Robotham,

I am in receipt of your letter of the 31st January.

I would be very pleased to collaborate with you and manufacture a Cylinder Head for the 3½ x 4½ unit.

In this size of Cylinder with a compression ratio of approximately 10-1 we would guarantee a fuel consumption of .45 lbs. per brake H.P. hour at maximum torque, but would expect a reading in the region of .4 lbs. per B.H.P. hour under favourable conditions. A.{Mr Adams} B.M.E.P. of about 150 lbs. per square inch would also be expected, depending on the temperature of the induction gas.

As a point of interest, I enclose a Power Curve (G.23) of a 4.1 litre 6 Cylinder Engine designed for heavy transport duty with expected and guaranteed performances.

In answer to your last paragraph, you will note that a power curve is given showing a B.M.E.P. of 143 lbs. per square inch, being the maximum figure obtained from the Engine in a stripped condition. The 132 B.M.E.P. figure is from the complete assembled power unit including a transport size Generator under full load and a cooling fan absorbing approximately 10 H.P. The barometer at the time was below normal and the temperature slightly above normal. Incidentally, this Engine ran with a very hot induction system, which also somewhat reduces the B.M.E.P. on account of lowering the volumetric efficiency.

With an Engine of our latest design, using reasonable induction temperatures, we can obtain B.M.E.P's up to 160 at standard atmospheric temperature and pressure conditions.

You may be interested to know that the 4¼ x 5 four Cylinder
  
  


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