[cjpacitto]

The pistons themselves are not alusil. Only the block is alusil.

As stated above, there is an iron oxide coating on the skirts to protect them from the silicon in the block.

I had my pistons done by Swain Tech. When I got my pistons back the additional thickness from the coating made them too large to fit into the cylinders. Yes, it's only a few thousandths thick, but the piston to cylinder clearance on these engines is very small to begin with. I had to hone my cylinders out a couple thousandths to get the proper clearance then finish with the Sunnen compound. After all that was done I discovered that standard piston rings were too small and had way to big of an end gap. Luckilly Lindsey Racing makes oversized rings for exactly this purpose.

BTW, both Swain Tech and Lindsey say coatings are compatible with Alusil blocks.