2001-2004 6.6L Duramax Cast Iron Cylinder Head (One) LB7 (110100101)Description 50 States Emissions Legal (E. O. D 701 38) The OEM Duramax cast aluminum cylinder heads fall short over time the different heat expansion rates between cast iron engine block and cast aluminum cylinder head cause head gasket scrubbing and eventually blown head gaskets. The aluminum cylinder heads are also prone to warping, melting, and or cracking in high performance applications where excessive heat is introduced. PPE's new LB7 Cast Iron