This topic is still bouncing around in my head, and likely will until I actually start to work on the exhaust (coolant system is taking way too long to finish). Regardless, I was thinking about the idea of individual one-per-cylinder exhausts that john hennessy threw out there. I initially dropped the idea due to the fact that it would add more weight and cost due to needing to add/buy more mufflers. But then I had a thought, the slip in muffler baffles are pretty cheap and come in a variety of lengths/sound reduction levels. Individual exhausts would be pretty straight forward so I decided to look into it more and came across this question/answer article from Cycle World. I thought it had some good input on the one-per-cylinder/4-1/4-2-1 debate so I thought I would add it here.
http://www.cycleworld.com/2014/01/03/ask-kevin-are-reverse-cone-megaphone-exhaust-systems-making-a-comeback/ Quote:
Rob Muzzy once remarked to me that if power is the only goal, individual, one-per-cylinder megaphones can’t be beat. The universally used 4-into-2-into-1 systems on inline, flat-crank fours may make a bit less power, but they compensate for that loss by suppressing to a useful degree the big torque flat spot that occurs at about 70 percent of peak-power rpm. The return wave from the expansion of the exhaust pulse normally helps evacuate the volume above the piston at TDC after the exhaust stroke, and this low-pressure wave then passes through the intake valve(s) and gives the intake process a torque-boosting head start, even though the piston has not yet gathered much speed on its downstroke.
But at lower revs, it is a positive wave that hits the still-somewhat-open exhaust valves around TDC, and it stuffs exhaust gas back into the cylinder and can even blow back into the airbox through the intakes. This reduces torque because what the piston draws in during the early part of the intake stroke is this exhaust gas, not pure fresh charge. The result is a flat spot that tuners have tried for years to eliminate, but it won’t go away. This is why no race tuners use a simple 4-into-1 pipe any more.
The answer is to make a 4-2-1 exhaust. The second enlargement that occurs as the two pipes join into the single collector generates a later-arriving suction wave that bucks out the positive wave that would otherwise shove exhaust back into the cylinder to create the flat spot. It’s not a perfect solution, but it has been widely used.
In MotoGP, the bikes are given a 130 dB sound limit, but in AMA, the limit is only 105 dB. When you have to meet a sound level, it’s lighter in weight to do the whole job in just one or two places—hence the can or cans you deplore!
Back when Honda and MV Agusta were racing air-cooled four-stroke bikes, Grand Prix tracks emphasized top speed a lot more than they do now, with most races taking place on “bullring” tracks like Jerez or Valencia, which jam all their length into small (cheaper!) real estate that can be seen from grandstands, with a multitude of first- and second-gear corners. The lower an engine is pulled down in rpm by having to use lower gears (wider ratio separations), the wider must be its flat-spot-free power range. In the old days, megaphones did a fine job with MV’s seven-speed gearbox and the many more speeds in the gearboxes of Honda’s smaller-bore bikes of the ’60s. On today’s courses, those bikes would go faster with 4-2-1s.
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