From Wikipedia:
A
Stroker kit is an aftermarket assembly that increases the
displacement of a
reciprocating engine by increasing the travel of the piston (that is, the piston moves further up and/or down in the cylinder). This is done by using a different
crankshaft where the crank pin is moved further away from the center of the axis of rotation of the crankshaft. While this increases displacement and
torque it can potentially lower the limit to which the motor can rev safely compared to the stock configuration
http://en.wikipedia.org/wiki/Stroker_Kit
Sorry, don't have much time right now. That should cover it well enough.