So I'm here looking.. do I go with cast or forged pistons.. I know why and how the stock piston ringland went due to too lean but that's going to be corrected when the motor is rebuilt.. my question is my cylinders and after 220k miles, I guess I can call myself lucky the piston with the ringland did not do much of any damage at all. But the thing is I don't think the stock A-B piston sizes will fit anymore?

The A/B sizes have to do with fit tolerances because of variations in the bore sizes. At the factory they bore both the cylinders on each bank at the same time with separate bore heads. The differences between the two are minor, but enough that a very slightly different sized piston will create a better fit.

 

When you have the cylinders re-bored (if that's the plan) they will all be done with the same bore head, one at a time, thus they will all be the same size afterward. New oversized pistons only need to match the new bore size. (0.25mm or .50mm over)

The A/B sizes have to do with fit tolerances because of variations in the bore sizes. At the factory they bore both the cylinders on each bank at the same time with separate bore heads. The differences between the two are minor, but enough that a very slightly different sized piston will create a better fit.

 

When you have the cylinders re-bored (if that's the plan) they will all be done with the same bore head, one at a time, thus they will all be the same size afterward. New oversized pistons only need to match the new bore size. (0.25mm or .50mm over)

the bore job would take care of the out of round and taper so if I have it right I should buy the pistons first then have the block bored to the correct size? If I'm correct I don't think Subaru offers stock pistons in nothing but stock A & B sizes? If they do I never seen a part number.

 

I was thinking at least 99.7 mm pistons to go with.

Edited March 20, 201610 yr by 1-3-2-4

You can do that as long as the block isn't scored. If the cylinders are scored or significantly out of round they may need to be bored larger than the standard 25 over. Have the block bored first, then order pistons to match the overbore.

Same with the crank and rods, have any necessary work done on them before ordering bearings to match.

You'll need to do your homework on this one. Some machine shops will require the pistons in hand for measurements before they can bore the case halves.

Ah gotcha well I'm going to have to see what they say.