Kibblewhite Precision Bronze Intake/Exhaust Valve Guide (+.001in.) 20-4321We choose to use C630 nickel bronze as a material to make valve guides because of its ideal characteristics for the application. The 4 5 percent nickel content provides superior resistance to wear, and the approximately 80 percent copper content delivers outstanding heat conductivity. Guide profiles are designed to have minimal effect on the airstream while maintaining critical cross sectional thickness in high temperature areas, promoting high