Well, I believe that getting the exhaust out to the atmosphere quickly and with velosity would improve the scavenging. When you have just the cutout uncapped, (like original) you lose velosity and the flow gets lazy. I believe especially in turbocharged applications getting the exhaust out quickly and with velosity is a must. Also I don't think the one turn is much of a restriction. Also the sound and flow is true open exhaust, not a big exhaust leak.
