For the ultimate in "Oval Port" performance, the fully CNC ported AFR 290 has no competition. With flow figures that most small to medium sized rectangular port castings would be envoius of, these high flowing "Ovals" produce tremendous air-speed and really pack a punch. Ideally suited for 396-509 cid street and strip performance, as well as circle track applications which require strong low and mid-range torque to help accelerate a car coming off a corner. Once again, AFR has included its trademark 3/4" deck, reinforced rocker stud bosses, and thick rugged castings, so you can own the strongest and most efficient heads on the market today. Premium hardware such as 2.250/1.880 one piece stainless valves, 1.550 double springs, 10 degree locks and retainers, and high quality studs and guideplates all come as standard equipment. Take note the higher flowing exhaust ports are raised .375 over stock location, and therefore these heads might not be a direct bolt-on in every applications. These heads have no EGR and are not emissions legal. Note: Optional stud girdle required for 2° rolled valve angles and 1" longer head bolts needed on four bottom exhaust bolt holes. Chevrolet Big Block - 290cc Competition Package Ported Heads, Assembled - 121cc Combustion Chambers