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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).
Reproduction and specifications of the 40/50 HP car ignition system.

Identifier  ExFiles\Box 181\M11\  img142
Date  12th February 1919
  
To EFC. from R.{Sir Henry Royce}
Copy to CJ.

ORIGINAL

12th February, 1919.
R1/G12219.

[STAMP: RECEIVED 1919]

X.2565
X.3129

RE. PRODUCTION OF 40/50 H.P. CAR IGNITION

I do not want you to make a new sized coil and cannot see any reason for wishing to reduce the ohmic resistance of primary in either coil, assuming that no damage by heat will occur if coils left accidentally in circuit with proper ballast resistance.

I am quite content with Al coil and think it is not at all necessary for the battery ignition with .5 make and break to go over 2500 engine revs. Wiser to be content with this equipment and the best resistance we can get supported on porcelain.

Can the battery ignition switch which is to be on the instruement board in future, have a red tell-tale indicator?

I fear a lamp is hardly practical though I suggested it. It would be located on the distributing board under the dash. If we use a lamp at all, it can be a 12 volt one preferably such as would be used on the car for lighting. An additional resistance is rather an advantage than otherwise, and might possibly be in parallel or in parallel series. [Handwritten annotation: resistor symbol, 'lamp, nicely red']

I believe you will find the existing cam quite right for .5 make ratio. There will therefore be very few new pieces to make for a 12 volt, six-cylinder, 2500 rev. ignition, with .5 make and break ratio (timer), and .5* (30°) distributor arm, with compression pressure like 7 CA, high tension wires grouped in lined metal tube, short circuit current not to exceed 2 amps;

(Contd.)
  
  


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