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The documentation states:

N does not raise the precision of approximate numbers in its input

163.0 (or 163., or 163` ) is a machine precision number, and Mathematica will not fake a higher precision when a certain number of digits are requested with N.

See this answer and this tutorial for more.

These questions may also be of interest:

Converting to machine precision

Annoying display truncation of numerical results

Mr.Wizard
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