Colyn said

Is that cube root (1+ (delta HP/HP))
or ((1+delta HP)/HP)


Pretty sure the intent is to take the cube root of a per centage change in HP, so that would be cube root (1 + (20/180))  not cube root (21/180).  The former gives about 1.0357 or a gain in speed of about 3.57%.  The latter would give about .4886 or a huge net loss in speed.

Tom