the bore is determained by the inside diameter of the sleeve. But the outside diameter is the part that will decide whether or not it fits into the crank case. My theory is that a 2.5 crank w/ a 3.3 sleeve and piston will give me more top end horsepower (created by bigger bore) without uncontrolable low end torque ( created by longer stroke of 3.3 crank). This would mean a very drivable rusty w/ blistering top end speeds.