Hey Tony, I hope this crude drawing helps you understand the question you had. All the answers so far are also correct. W8ye had the reason I think you were looking for. I think the greatest "feel" of the compression difference is from the pistons running clearance & its changing sides from the engine being rotated by the crank. (or prop) While the engine is running however, it is the piston that moves the crank in the power stroke. In the right hand drawing, the force of the piston tranfered to the rod will cause the piston to the intake port side of the wall & will help to seal the ring gap better while running. As far as a right or wrong way to install on a 4-stroke, It might help to put the gap on that side of the piston. But I have seen some rings rotate within the cylinder depending how tight of a fit they are. So it really wont matter in those case's. The gap is so small & the speed of the piston is so great, that while running, there is not much time for much leakage to take place. In a perfect fit, (no gap) there would not be any room for heat expansion & the trouble that would cause would be bad. Also, in a 4-stroke, it is through this gap that the engine will get its lubricating oil. They tend to be a little larger in gap than a 2-stoke engines ring. Hope all this helps, Bill