Type 4 Spark Plug Wires, ThunderCore Ultra, Made in USAThese USA made Type 4 wires fit the '72 and later Type 4 engine, found in the late buses and Porsches. They are the best qualty we can find on the market. The silicone outer jacket surrounds an EPDM inner insulation layer. The high quality copper core provides high temperature durability. Since they are copper core, they should not be used with the Ignitor 2 or Ignitor 3 product lines, but are great for use with the Ignitor 1's.