Each detonation creates an exhaust pulse. The faster the pulse is, the more of a void is left behind. This void creates a vacuum. The vacuum assists with drawing in fresh air and fuel, on the intake cycle. This is called scavenging. In a 2-1, one pipe is able to help speed the velocity of the others pulse, and visa versa. True duals rely solely on their own exhaust pulse. Remember, your engine is basically an air pump. More air in, more air out. The 2-1, is hands down, the best exhaust design. Then 2-1-2, and lastly, true duals. Baffle size, also plays a major roll. Contrary to belief, a wider opening is not always best. Also remember, you’re shooting for velocity. Too wide, and you create turbulence, which is bad. Think of it like this; when you blow out a candle, do you you open your mouth as wide as you can? Or do you pucker up and blow?

You are NOT seeking back pressure. You are seeking VELOCITY for the escaping exhaust gasses. While the torque cone does help with velocity for a short run within the exhaust system, the exhaust pulse slows down again once it reaches a wider part of the pipe. Thus, defeating the exhaust’s pulse velocity and the scavaging effects of the vacuum left behind the pulse.