cleaning the carbon from the pistons I pulled from My L28...and they say Y34 on the top. I wouldnt have thought anything of it, except that one piston is differetnt, it says 'std' and appears to have a deeper dish than the Y34...any ideas which is the standard L28 one and where the other type came from ?

PUlled the head from another standard L28....this one had '23' printed on top of the piston head....now Im even more confused

The L28 has a number of build combinations because of diffrent heads blocks cranks and compression, these are caused by production changes mainly to meet polution control targets in diffrent markets. What you are seeing is some of the spread that makes up the combinations. The main deviation is for head combinations and some pistons will not run well together in standard form, If you fit a P90 head to an purely N42 built engine it will drop the compression out from about 9 to 1 and give you about 7.5 to 1 great when you fire up the garret but a slug when normally aspirated without any modification. To find variation in pistons under the same head comes down to poor or sloppy work practice. It seems to me if you check the cylinder with the rogue piston, it will have a diffrent bore measurement as well. sounds like Someone repairing on the cheap at some stage.

good luck

my 2c

Steve

yeah, pretty much figured the same.

Oh well, I now have a complete set of the SAME pistons (23 on these ones) in the block