Shown with optional riser bung. These high performance manifolds are unique in design, that creates a high velocity airflow that increases torque, rpm, and horsepower over stock cast iron manifolds. We have experienced 40-50 foot pound of torque on bigh block 502, 415 horsepower motors, and 80 to 90 foot pounds of torque on engines up to 575 cubic inches.PowerFlow manifolds are water-jacketed, water surrounds each exhaust passage, including the ports to eliminate burnout. Black manifolds are hard anodized prior to powder coat, to ensure against corrosion.Big Block Stainless steel ”A” risers are designed for stock Mercruiser Bravo exhaust tip locations. 3/4"npt fitting is used on front of pipe for thermostat housing that have (4) 1" hoses water to go to exhaust manifolds if needed click on (ADD BUNG).The risers are highly polished stainless steel, and are designed for 4" exhaust tips. We offer a wide variety of riser pipe configurations to accommodate just about every application. Custom riser pipes can also be manufactured