Header explanation? Please

Header diameter and length depend on the motor you have as to horsepower and torque. The smaller dia and longer length will yield more lower end power (torque) but again depending on the motor. A high revving motor with more cam and compression will want a larger dia header and a some what shorter length. As far as tuned all the tubes will be of equal length. I hope I am correct Bill. Maybe perfweld will chime in as he builds headers for a living.