AFR's LS1 head offers unmatched flow performance (300 CFM at .600lift) and features 2.020 intake and 1.600 exhaust valves with AFR's iron ductile interlocking valve seats. With only 205cc port volume this is a 70 CFM increase over stock casting. The 205cc is ideal for normally aspirated 346C.I. to 396C.I. It is available with 66cc and 76cc combustion chambers. AFR's LS1 is a direct bolt on. Structural features like AFR’S trademark 3/4" thick head deck, reinforced rocker stud bosses, and thick wall runners provide unparalleled durability. An exclusive new modern combustion chamber design with double quench pad area helps the LS1/LS6/LS2 generate huge low and mid lift airflow numbers Note: Hydraulic roller cams in "LS" Gen III engines typically experience valve float at 6600-6800 RPM's. If you plan on running over .600 gross valve lift and/or 6600 RPM, our upgrade spring has higher seat and open pressures (145/390+) to better reduce the risk of valve float in more aggressive applications.