There is a reason for going to twin pipes; there are many that I have come across that argue that it's pointless but I have read a book on the scientific design of exhaust systems that state, in several chapters, that strongly recommends the need to keep exhausting and intaking cylinders apart. Pulses that travel from exhausting cylinders flow into intaking cylinders during that brief overlap period pushing exhaust fumes back into the cylinder thats trying to push out all the spent gasses. Keeping cylinders 1, 2 and 3 appart from 4, 5 and 6 does have andvantages. I still intend on building my twin "quiet" setup once my good motor is built. They used these systems in Japan many years ago as did the BRE Datsuns...