Kevin,
What is 51? LOL
The only numbers I could come up with after looking at it a while.
Subtracting your .050'' duration from the .006'' gives a value of 51 on both the
intake and exhaust side.

Intake: 274* - 223*
Exhaust: 276* - 225*

Some use this to get an approximation of the acceleration of the lobe. Lower
numbers indicate a faster ramp rate as the lifter travels the cam lobe pushing
the valve open from .006'' (opening) to .050''.

The 226 profile has a value of 49*... XE-R lobes are pretty 'quick'.