Yes, there's a high end performance issue, but I think that Ja-moo was making reference to a narrower powerband which is easier to live with a on a sled than a bike.
I have looked at sled pipes on twins and triples and one characteristic they share are extremely short headers. Modern combo pipes on sleds have very short headers that are also tapered. Without testing, my hypothesis is that shorter header section reduces loss of energy in the returning waves and teh taper helps to prop up the top end.
The software I use doesn't support 3 into 1 pipes and the only simulations I have seen using the more expensive package did not track well to reality in that 2 into 1 design. Whether that's a data input error or software shortcoming I have no idea.
There are two fundamental issues in a 3 into 1 pipe. The first is the collector which has to be long and smooth to aid gas flow and short so as not to disrupt wave formation. That will be a compromise regardless.
The second issue is wave timing. When the port open, a high pressure wave travels down the pipe, as it travels down the divergent nozzle, it is reflected back as a negative wave to help evacuate the cylinder. As it travels down the baffle cone, it is reflected back as a positive or stuffing wave.
With a 3 cylinder motor with exhaust timing of say 90 degrees BBDC opening and 90 ABDC closing, that low pressure sucking action lasts from about BDC through to just before the port close at which time the stuffing wave arrives just before the port closes. So - high pressure 90BBDC to say BDC, Low pressure BDC to say 70ABDC and then stuffing wave 70 -90ABDC.
Still with me? Good.
The timing issue is that there is 60 degrees of overlap between any two cylinders. One is closing 60 degrees after another exhaust port opened. That means that at resonant frequency, one stuffing wave arrives just as the next cylinder is still emptying, so it makes it harder for that next cylinder to empty effectively. The negative sucking wave from that second cylinder is now getting back as the first expects a stuffing wave, so both actions are diluted and the pipe is not effective.
At much lower revs though, things are different because the waves are all arriving early. Wave pressures are much lower amplitude, so they are less disruptive to the other cylinders.
Just working out when waves arrive on three different cylinders at different speeds is enough to cause acute brain fade.
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