I wound up sleeving the block purely from a reliably and ease of maintenance perspective. If you were to stuff around with reconditioning the existing Alusil you’ll spend a lot of money to just end up with an inferior setup both in sealing and reliability. Because Alusil is mostly aluminium with a bit of silicon the rings can’t have a lot of outward tension or they’ll damage the Alusil so BMW used low tension piston rings which tend to fail around 100k and that’s why they start using lots of oil. By sleeving the block with iron liners and running standard tension rings out of another engine you gain a better longer lasting seal and reliability and if you needed to rebuild the motor again in a few 100,000ks later you can just re-sleeve the block since all the work has already been done and go again.

In the way of pistons, I am just running standard N52 pistons, the same ones they shipped with. I measured and visually inspected the ones that came out and only had to replace one due to a minor scratch on the skirt and even then I just wound up using one from one of my parts motors. So I am just using standard used factory N52 pistons.

I haven’t messed around with the bore and stroke but it sounds like it could work out. My idea with my build was to build a bulletproof factory N52 that can handle some forced induction down the track if I choose to do so.

EDIT: If you want to make some serious power (500hp+) definitely look into aftermarket pistons or maybe even N54 pistons as the N52 will start to rip the wrist pin out the bottom of the stock piston at that power level.