When you need 5 to 10 HP.
There's a reason that many of the top teams in Pro Stock, Comp, and Super Stock use Dynatech high velocity merge collectors. They feature the optimum reduction angle to increase torque and add 5 to 10 HP. They're 100 percent TIG-welded, high temperature silver ceramic coated inside and out, and feature jig located U-tabs for bolt-on collectors.
Header Collector, Mild Steel, Bolt-On, 2 1/4 in. Primary Tube Diameter, 4.00 in. Collector Diameter, Each