The Edelbrock Performer RPM Aluminum Cylinder Heads feature threaded inserts in the rocker studs and exhaust manifold bolt holes for superior strength and durability. This complete head includes stainless steel, one-piece, swirl-polished, hardened tip 2. 09 intake and 1. 66 exhaust valves. They offer improved power throughout the RPM range for greater throttle response and top-end horsepower. These 428 Cobra Jet-sized valves promote excellent flow for streetable power and will clear 4. 050" bores on 390 engines. These cylinder heads feature 72cc combustion chambers, are not port matched or bowl blended, and are designed for stock replacement valves. The Rocker Shaft Stud Kit #6009 provides better rocker shaft retention and is highly recommended for use with the Edelbrock FE heads. It eliminates wearing of the threads and the possibility of bottoming the rocker shaft bolts in the head.