Let me try to explain this better.The compression calculator only reads the top of the piston in relationship to the cyclinder ie:in the hole or out.So .018 out of the hole is the same regaurdless of the stroke.the compression is raised by the calculator by going from TDC to TDC as the piston will only be .018 out of the hole.You couldn't use the kb243 with a 4"stroke as it would be out of the hole probably past the top ring so a piston with the pin closer to the top of piston would have to be used but it could still end up at around .018 out of the hole if the right setup is used but that was 13:1 in my set up.Certainly not a pump gas combo.Most use the dish pistons to keep the CR under 10:1.