Edelbrock Polished RPM Air-Gap BBC Rect Port Intake ManifoldEdelbrock part #75621 RPM Air Gap 2 R intake manifold is designed for street 396 502 c. i. d. Chevrolet V8's with high performance rectangular port heads. The open air space separates the runners from the hot engine oil, and as a result, the air fuel mixture stays cooler for a denser charge and more power. This intake manifold is a dual plane, high rise design with a 180 degree firing order to produce incredible top end horsepower while retaining good