Improve Your Fuel Efficiency and Horsepower with Performance Products Engineered Spark Plug Ignition Wire Sets By Karlyn/STI Our European wire sets are made with the finest copper core silicone wire which greatly exceeds O.E. and competitor specifications. This double extruded Silicone-over-Silicone wire contains 19 strands of tinned copper core which provides "super conductivity" with superior corrosion resistance.