Trick Flow engineers used the best features of OEM GM LS3 and LS7 cylinder heads, combined with their own race-winning engineering and technology, to create the GenX® 255—the ultimate ultimate square port LS cylinder head for 4.000" and larger bore engines. The heads feature fully CNC Competition Ported runners with a premium high resolution surface finish for maximum airflow and performance potential. Stock LS3 ports accommodate LS3-style intake manifolds and LS9/LSA blower assemblies. The valve angles have been changed from 15° to 12° to increase piston-to-valve clearance and allow the use of larger camshafts. The coolant holes through the head deck were redesigned to work with all LS head gasket and engine block combinations. GenX 255 heads are available with standard or 6-bolt per cylinder mounting patterns. Trick Flow GenX 255 cylinder heads are emissions-legal under CARB E.O. #D-747 for 2007-present GM vehicles with 6.2L engines. They are available fully assembled or as bare castings. Sold individually.