Quote:
Originally Posted by DWalt
The CUP measurement understates actual peak chamber pressure measured using a piezo gauge by 15%-25% depending upon many factors. You can think of the CUP as being an approximate "average" pressure due to its very long time constant (response time). On the other hand, piezo gauges have a time constant of essentially zero. CUP is an obsolete technology best left in the history books than depended upon for any purpose today.
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While CUP measurements may understate pressures, if they are used as a gauge of where to draw the line, that is not an issue. The problem comes when you try and use them interchangeably. I understand that the newer technology is superior, but the old technology was effective within it's limitations.