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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).
Comparative analysis table of various engine cylinder heads with performance metrics and a brief conclusion.

Identifier  ExFiles\Box 134\2\  scan0054
Date  30th October 1935
  
- 3 -

Hs{Lord Ernest Hives - Chair}/Wd.{Mr Wood/Mr Whitehead}1/GB.30.10.35.

CYLINDER. | Drg. | Valve dia. | RPM. Factor. | Piston Speed Factor.
------------------------------------------------------------------------
Kestrel .......... E.40267 | 1.62 | .45 | 2.47
P.V.G. Ramp ........ E.42879 | 1.62 | .65 | 3.56
Steel Penthouse .... EX.14463 | 1.75 | .70 | 3.85
" " .......... " " | 1.42 | .45 | 2.50
------------------------------------------------------------------------
P.V.12 Pancake Head . D.2684 | 1.7 | .43 | 2.58
" Exh. Plug Ramp D.3070 | 1.8 | .57 | 3.42
" Inlet " D.4000 | 1.8 | .55 | 3.30
" " "mod." LeC.4577 | 1.8 | .58 | 3.50
------------------------------------------------------------------------
Bentley Ramp 1 .....LeC.3739 | 1.5 | .67 | 3.00
" " 11 .... LeC.3871 | 1.6 | .73 | 3.30
High Power 1 .......LeC.4075 | 1.75 | .76 | 3.42
------------------------------------------------------------------------
Rudge ..............M.3491 | 1.18 | .86 | 3.00
------------------------------------------------------------------------

From these figures of merit the Rudge would have the highest R.P.M. at peak power and the steel penthouse would have the highest piston speed at peak power, the Kestrel being the worst head tested on both counts.

A wooden model of the ramp head Kestrel was tested and found to give about 4% greater flow than the actual head.
  
  


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