Cummins single cam Compact Graphite Iron (CGI) Cylinder Head Stage 3Compact Graphite Iron (CGI) cylinder heads are manufactured with a distinct molecular structure from traditional gray iron cylinder heads. CGI exhibits significant advantages in high heat and high stress applications due to its 75% increased strength and enhanced thermal conductivity compared to standard gray iron heads. These are not the same heads you see advertised everywhere else, They are much better. They are fire ringed and it sits just outside