--I talked with a knowledgeable and experienced person this weekend regarding the 11-12 Pro cylinders/pistons. As a dealer, he had many Pro engine failures, mostly 11's, and a lesser number of 12's. His take on the issue is tolerance stacking.
--The cylinders can be moved around a bit when installed on the case and, if installed a little forward, creates a gap between the rear skirts and the case, thereby giving no support to the skirt itself. The skirt then fatigues and breaks. The gap can be larger or smaller depending on the machining tolerances and location of guide pins, bolt holes, castings, installation, piston tolerance, etc. So, before you torque the cylinders down, make sure they are pushed back as far back as they will go and keep your fingers crossed.
--Apparently the 13 cylinders have thickened skirts and maybe closer tolerances between skirt and case.
--"If" tolerance stacking is a primary issue, that would explain why some motors go at 500 miles, others go at 1200 miles and others seem to run ok.
--He also mentioned stock pistons may work ok but do not match the cylinder porting very well. Tolerances can also vary. Loose pistons in a loose tolerance engine=kaboom. This may partially explain why, for example, an RKT drop in piston kit gives a boost in power.
