Long tube designs 30+ "'s create a strong exhaust pulse signal throughout the piipe which enhances low-to mid range torque and hp. As the tubes become shorter ie, shorties ir mid-lenght haeders, the tuning effect has less time to enhance the engine low speed benefits. A shoter header tube will allow the low-to-mid power to fall off while increasing the upper end potential of the engine. Basically tube lenght can and is used to alter the power curve of the engine. Another critical factor is primary size. I'm not going to go into detail there but you can go too large, but i doubt the pacesetters evryone uses are too big. Header choice should depend use of vehicle.. So shortie headers will provide an hp/tq increase and I've got dyno number to prove but no scanner to put on post. With shorties, k&n drop in MPFI spacer, and magnaflow cats i pivked up almost 30 hp