The most well-known example of this was the Chevrolet Vega’s hypereutectic engine block cast out of Reynolds A390 (now known as Kolbenschmidt’s Alusil). 

Lokasil was used in Porsche Boxster, Cayman, and 911 models from 1997-2008; Alusil cylinders have been used in many Aircooled and watercooled Porsche engines including the 2.7 and 3.0 SC, 944, 968, 928 and most recently, Cayenne, Panamera, Macan, and sports car models with the 9A1/MA1 engine.

So, what makes a hypereutectic cylinder different than one that is Nikasil plated? Where a cylinder or block might be Nikasil plated that provides a hard coating comprised of nickel, silicon, and carbide, Alusil and Lokasil cylinders have raw aluminum bores that require special preparation to expose the silicon particles present in the aluminum. The pistons are then iron coated to provide a barrier between the aluminum bore and aluminum piston skirt.

The oil film on the cylinder bore surrounds these silicon particles and forms the tribofilm that supports the piston and ring system. Formation of this tribofilm is critical to proper operation of engines with Alusil and Lokasil cylinder bores (and why choice of oil is so important).

One of the tools that are invaluable to evaluating cylinder bores is a profilometer. Not understanding the importance of proper surface finishes and measuring them can lead to problems when rebuilding any engine. 

Lake Speed Jr. and Charles Navarro in this installment on bore scoring evaluate surface finishes using the Mitutoyo Surftest SJ-201 profilometer in evaluating cylinder bore scoring failures. You can read more about Al-Si cylinder systems and bore scoring including Porsche engines with Alusil and Lokasil cylinder bores at https://lnengineering.com/products/watercooled-porsche-cylinders-sleeves-and-pistons/bore-scoring.html.