Tomei - Valve Guide Set CA18DET (TA309A-NS11A)Tomei decided to make there Valve Guides from Phosphor Bronze (Cn Sn P alloy) for its highly tensile and superior heat transferring ability which is vital in high power and high RPM outputting engines. Since race engines these days require more power at higher RPM use with leaner AFR mixtures, these engines now experience more extreme heat conditions which risk with the rapid deterioration on these valve train related components. The Phosphor Bronze