Designed for 302, 327, 350, and 400 c.i.d. engines up to 1986, these heads have the same powerful design and combustion chambers as the straight plug Performer RPM heads plus an exhaust crossover passage for emissions equipment compatibility. These 50-state street legal heads work with the Performer Power Package and provide outstanding street performance. Performer heads with 64cc combustion chambers improve performance and retain stock compression ratio on 1970 and earlier small-blocks. Hardened pushrods required. When using hot air choke carburetors and Performer manifolds with these heads, choke kit #1932 is required.