Hooker Adjustable race headers allow you to change your header primary tube lengths, collector lengths and diameters and collector types (Classic 4 into 1, Merged and Split-Flow). By altering the relationship between the primary length and collector diameter and length it is possible to increase or decrease the torque and horsepower output at any specific R.P.M. level. For a slick track the header primaries or collectors can be shortened to decrease the low end torque for better traction. Larger diameter collectors will also reduce low end torque. On a good track with lots of bite, extending the primaries or collectors will pick up bottom end power for a harder launch and awesome e.t.'s. Smaller collector diameters will also increase low end torque. Hooker adjustable headers have taken more Pro Stock drivers to the championship than any other brand.