Yes, they all have the same bore but the geometry SUCKS on all but the 170.
The bore being too small for the stroke, essentially means that the power pulse will not have enough oompf to work the crank with any sort of anger.
Add the long rod into the equation, and the power pulse is being used up too soon in terms of crankshaft degrees to generate any effective torque.
Also, the lack of angularity with the long rod means that power pulse is being used up during the least effective phase of the rotational cycle.
Things don't really come into sync with the 225 until around 3500 rpm
