2 strokes will always make the most horsepower with ONE individual expansion chamber per cylinder.
As soon as you add 1 or 2 more cylinders to the mix, the soundwaves (for lack of a better explaination) begin to collide in a way that disrupts the whole purpose of an expansion chamber.... Cramming unburnt mixture back into the cylinder before the port closes.
There is a guy working on a 3 into 1 for a Kawasaki Triple that will have interchangeable "chambers".. all made to work at different RPM's. It will be pretty cool to see how it all turns out.
Ive had a few different old-school brands of 3 into 1's on H1's and H2's and they all work the same... Good low end and midrange grunt......but at 6 grand or so, absolutely shut off like you are hitting the kill switch. 6 grand on a triple is where the fun is supposed to start, not stop.
Ive also ridden a buffalo with one of Omar's 3 into 1's and it ran well. Buffalo's were never high revving, so you didn't really miss that last 1000 revs.