We may have heard the term Nikasil that’s associated with Porsche, but why?
Nikasil was original developed by MAHLE in 1967 along with the NSU car company, primarily to help prevent wear in its aluminium rotary engines. Aluminium is a light but soft material, meaning that in areas such as cylinder linings a more resilient material is required. Because of this, chrome plating, iron or steel liners were all used to prevent bore wear.
MAHLE’S solution was to create nickel silicon carbide, or Nikasil. Silicon carbide is a tough ceramic, but MAHLE dissolved it in nickel, a material that resists corrosion and is commonly used in plating another metal for protection. By using the nickel cocktail to carry the rugged silicon carbide, components such as cylinder linings could then be locally electroplated with the mix. Once successfully plated, the piston rings then rub the cylinder wall, abrading the cover of nickel away, leaving behind the silicon carbide. This hard coating, just 0.07mm thick, then protects the softer material underneath, but also helps promote lubrication because the silicon carbide particles collect oil.
Porsche’s rst use of Nikasil dates to 1971 with the 917. Along with the widening of the 917’s bores, the 12 cylinder linings swapped from using chromeplating to Nikasil coating. Using MAHLE’S treatment enabled Weissach to use tighter manufacturing tolerances in the 917. Aside from the coating, this tighter seal in the cylinders is partly a reason for the 917’s increase in power to 620bhp.
In 1973 Porsche carried the technology over to its road cars on 1973’s
Carrera RS 2.7. Here, the centrifugally cast alloy cylinders had their cylinders electroplated in Nikasil. In 1974 Porsche introduced Alusil, a cheaper alternative to its predecessor, which involved etching the coating to the bores instead of electroplating. Alusil is a similar idea, but instead of applying the silicon, the engine block is made with a high silicon content. The cylinder walls are then etched away to expose the hardened material where needed. From 1997 to 2008 Porsche also used Lokasil, another idea using silicon, but this time suspending it within a resin to form a tube. With Locasil, a tube of composite is cast into the block. The dierence between the two is that Alusil carries silicon throughout the block material, whereas Locasil is still an aluminium block, with the silicon-rich composite tube in the cylinder walls. Of the three, the most durable is the oldest.