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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).
Performance graph and analysis for raised crown pistons, showing Mean Effective Pressure and Ignition Advance against RPM.

Identifier  ExFiles\Box 123\5\  scan0283
Date  1st March 1939
  
-5-
④ As Curve ③ WITH PD 304 RAISED CROWN PISTONS AS DESIGNED
7:1 COMP. RATIO
MAX. POWER
x---x NON DETONATING
MEP lbs/sq"
MEP
IGN
* IGN ADV °BTDC
RPM
Curve (4). This condition is as Curve (3) but incorporating raised crown pistons PD.304, which raises the compression ratio to 7.0 : 1. This gives a good MEP curve with a maximum of 130 lbs/sq.in. at 2000 r.p.m., but is very bad for detonations and necessitates losing 15-20 lbs/sq. MEP to be clear.
Continued.
  
  


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