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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).
Electrical laboratory experiment testing the effect of spark plug electrode design on firing voltage.

Identifier  ExFiles\Box 162\1\  img043
Date  19th September 1938
  
ELECTRICAL EXPERIMENTAL LABORATORY.

From Rm{William Robotham - Chief Engineer}/AC.

19.9.38.

Experiment:- Effect of Plug Electrode Design on Firing Voltage.

Conclusions:- Plug requiring least voltage. Champion L.B.8.
Plug requiring highest voltage. Lodge three point.
The voltages required by the KLG and Lodge single point plugs are practically equal.

Rm{William Robotham - Chief Engineer}/AC/JJ.

Test Procedure and Results.

Four plugs of entirely different electrode design were fully tested under all round conditions on J.B.IV.
These plugs were:-
KLG.PLB.30X.
Lodge. 640 Single Point.
Lodge. 641 Three Point.
Champion L.B.8.

Each plug was tested in No.6 cyl. at gaps of .020", .025", .030", .035" and .040".

The firing voltages were measured using a Lucas portable H.T. voltmeter and the attached curves drawn from the results obtained.

For the whole of these tests a negative H.T. supply was used.

As can be seen from the curves the Champion L.B.8 gave by far the best performance, the plug requiring the highest voltage being the Lodge three point.

Rm{William Robotham - Chief Engineer}/AC/JJ.
  
  


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