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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).
Page 2 of a report detailing the specifications and performance characteristics of a six-cylinder engine.

Identifier  ExFiles\Box 22\4\  Scan088
Date  30th March 1927 guessed
  
contd :-
-2-

The engine - a six cylinder - has a bore X stroke
of 2.95" X 5.125" the swept volume being 3.444 litres or 10%
greater than the Goshawk.

The compression ratio is rather high being 5.9 /1
but the engine is not noticeably bad for detonations when oper-
ating on the dual synchronised ignition. Detonation is manifest
at low speeds but we do not think as bad as the 20 HP. when
running with a compression ratio of only 5.4 to 1.

This engine possesses very similar characteristics
to our own engines in being remarkably free from detonations when
the cyl. jacket water temperature is cool - below about 40°C.
It is found that the synchronised ignition besides requiring
appreciably less advance than single ignition, reduces the tendency
to detonate at low speeds. It will be remembered this character-
istic was marked in the case of the Hispano as well as with our
own aluminium Phantom with the turbulent type head.

The power output and consumption curves are given
on prints Nos. 4 and 5.

The peak of the power curve occurs at approximately
2750 r.p.m. similar to the 20 HP.

The B.M.E.P. curve rises to a maximum value at
about 2200 r.p.m. giving 107 lbs/sq.in. This does not seem
particularly high considering the high compression ratio because
the Hispano gave 111 lbs/sq.in. with a 4.6 to 1 comp: ratio. It
is however accepted by various authorities that the output per
unit volume increases with increase of cyl. dimensions, contd:-
  
  


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