SPELAB Exhaust Header for Chevy SBC Small Block Hugger Replacing or upgrading your exhaust header is necessary for both engine performance and sound. Whether on or off the track, exhaust headers provide more horsepower and improved exhaust sound. SPELAB offers many products to help you create your own custom engine headers. It's really easy and convenient to use: direct bolt-on, no modification needed. --Made with 1 5/8" OD diameter heavy-duty mandrel bent 18 gauge tubing--Large 2 1/2" collectors. Reducers are 2"--4 1/4" length from the bottom edge of the head to the outside of the middle tubes--Made with thick 5/16" flanges to resist warpage Fitment: Fits All Small Block Chevy V8 Engines from '55+ using the Standard Exhaust Pattern - 283, 305, 327, 350, 400, etc. (except 1971 Chevrolet Nova,1972 Chevrolet Caprice，1983 Chevrolet Caprice Classic Sedan 4-Door 5.0L,1984 Buick Regal,1986 Chevrolet Caprice 5.7,1987 Chevrolet Caprice,1978 Chevrolet Corvette, 1973 Chevrolet Nova Base 5.7L 350) Specifications: Brand Name: SPELABCertificate: ISO9001:2000Application: Automobile Exhaust HeaderMaterial: Stainless SteelSurface: Mirror PolishModel:EH28030 Inlet/ Outlet: 1.5"/ 2.5"Primary Diameter: 1-1/2 in.Collector Diameter: 2-1/2 in.Head Flange Thickness：3/8 in. (9.5mm)Pipe Thickness: 16 gauge (1.5mm) Exhaust Header VS Manifold, which is the better choice? The structural differences between exhaust headers and manifolds are the material and size. From the material, exhaust headers are made of lighter, thinner steel, while exhaust manifolds are made of thick iron. Exhaust headers are also longer than exhaust manifolds. When in use, exhaust manifolds create back pressure, which lowers performance. Because each cylinder of the engine is given its own tube, however, headers eliminate this problem; thus, allowing the gases to exit without the creation of back pressure. Therefore, exhaust headers are a BETTER choice than an exhaust manifold. To maximize the airflow gains from this exhaust upgrade, we highly recommend pairing it with our high-flow Small Block Chevy (SBC) Intake Manifold to balance your engine's breathing