My question is what would sticking 2.6 heads onto a 3.2 do ? I'm guessing the chamber is smaller than a 3.2 so would still raise compression so why not use these instead... Or is it the 2.5 are smaller again allowing higher compression than a 2.6 head ......
EPC says the X25XE and Y26SE share the same cylinder head part numbers, including valves, springs and camshafts. So it appears to me the engine top end is identical.
Con rods are the same too, and EPC lists the same crankshaft p/n, so stroke must be the same although the bearing part numbers are different for some reason? However, the main difference appears to be that X25XE blocks use 81.6mm diameter pistons, whereas Y26SE uses 83.2mm diameter pistons. That's a 3.96% increase in surface area so for the same stroke it raises a 2.5L to 2.599L. So looks like a simple block overbore job to me. It therefore follows that any reduction in compression ratio must be due to lower piston height.
Never seen either in real life, but that's what the part numbers say.