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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).
Engine testing methods, focusing on single-cylinder induction systems and valve timing issues.

Identifier  ExFiles\Box 134\1\  scan0007
Date  12th July 1937
  
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The two methods were compared, and appeared to check up fairly well. The second method, however, is sometimes liable to an error due to surging in the pipe leading to the U-tube.

This was got over using an arrangement as shown, the shaded item being a felt pad, which, apparently, had a damping effect and gave improved results.

It would appear to the Writer, however, that this method is open to criticism in that the felt pad may tend to act as a partial non-return valve, giving a rather higher reading than is correct, the best plan would be to check the two results, and see whether the same answer is obtained.

As far as actual lining up of single cylinder work with main engine work goes, there has been very little done except on Diesel units, where, as might be expected, no difficulty has been encountered, results appearing to repeat very well. In petrol engines, however, induction troubles arise, and the following points were brought up in discussion.

(1) On the single-cylinder unit, ramming characteristics of the induction system were altered by the valve timing. This brings up the rather serious point, that to evolve a main engine timing from the single cylinder unit, it may be necessary to repeat the process of compression pressure tests for each valve timing, due to the fact that:-

(a) the valve timing alteration will change the compression pressure of the bare cylinder.

(b) the ramming characteristic of the induction system will be altered, thus changing the power output of the engine due to possible supercharging effect. This power change will not necessarily be due to the valve timing in itself, but may be due to the valve timing having altered the ramming of the induction system, which in turn may alter the power output, giving entirely false results.
  
  


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