[tubman]

To follow up on what "Ol' Ron" posted, it's perfectly alright and actually beneficial to leave the fourth (bottom) ring off of the pistons if you have the rotating assembly balanced. I did on my last build an everything is fine. SWord has it that some engineers Ford borrowed from Studebaker (or was it GM) added it to solve an oil consumption problem. Modern ring technology has that whipped, so the fourth ring is superfluous.