Ok... well a .28 only has a larger bore and MAYBE a slightly longer stroke. T.... The case is no bigger, i mean C'mon how would you bolt it in if it was? if anything it may be .1 or .2 mm bigger but wheres the advantage in that?. i would think the advantage would be a thicker sleevve making the motor more durable and then being able to take advantage of the new porting in the .28