Calling All Mechanical Geniuses

I think anyone that says the motor needs back pressure doesn't understand what's happening or why. Back pressure is a by product of a properly designed exhaust system. When the exhaust valve opens, the pressure in the cylinder moves into the lower pressure area of the exhaust system. As the pressure drops, and the piston starts moving up, the pressure in the cylinder resists the piston's upward travel, reducing net HP. Less back pressure would reduce this, but there is also an intake charge about to happen next, and it starts while the piston is still moving up in the cylinder. The exhaust gasses have mass, therefore they have momentum. When the exhaust gasses travel down the pipe, they want to keep moving in that direction. This phenomenon is used to create a lower pressure area in the exhaust system, and that lower pressure area travels backward toward the exhaust valves. Exhaust manifolds have primary runners that are too small, too short, and of varying lengths, to be of any benefit as far as tuning goes. The only thing they have is back pressure. With a header, the tubes can be of a large enough size, and long enough length to cause the backwards moving pressure wave to hit the exhaust valve when it opens at a realistic RPM. Velocity has a greater affect on inertia than mass, so whereas the same amount of exhaust is moving through the exhaust system, the one with a faster moving exhaust will have more inertia. This is where primary tube diameter comes into play. A smaller tube causes the exhaust to move faster, have more inertia, and create a larger negative pressure wave to be created. As RPMs increase, more and more exhaust moves through the primary pipe, increasing back pressure to a point where it cancels out the benefits of the negative pressure wave. The length of the primary pipe has the affect of boosting power before or after the torque peak, which was determined by the primary pipe diameter and CID of the motor. A slower running motor has more time between exhaust pulses, so a longer tube gives the pressure pulse more time to reach the exhaust valve. A shorter tube gives the pulse a shorter distance to travel, so it would be tuned to a higher RPM. Velocity is the key, and is controlled by the tube diameter. A smaller tube has higher velocity, but adds pressure to the system. The back pressure itself is of no use. That's as much as I understand. Could someone explain collector size?