Do not use p29 pistons on a y4 or y8 head they have a totslly different head design compared to d16y1s. The pistons that are the best for the d16y heads are p06 or pg6 (ccant remember off the top of my head). If u decide to use p29 pistons make sure u buy npr(nippon racing) p29s as they have been redesigned to allow my clearance for the valves while still achieving a zero deck height. im acutally in the process of builing a 13ish comp d16 so if you need more info shoot me a pm