Well the usual reason you see slightly better performance from cans or something like your buddy built is due to lower restriction. Some of the in-cowl muffs out there are really not much good at all. While the length of the header tube on a full pipe system is critical along with the total length and positioning of the pipe's internal components, it doesn't do anything for the performance on a can.
Example is my ZDZ-50NG. I initially set that up with a SlimLine inverted Pitts type muffler after having tried the BCM on another model with a 50. SlimLine does not advertise a muff for the ZDZ-50, but the muffler for the DA-50 is interchangeable with the ZDZ. I had numbers on that engine for RPM, temps etc. and installed it on another model which was setup for a canister since I wanted to try it.
It is quieter, but I'll tell you that it is really disconcerting to not be able to hear the engine on downlines and so on, then there's the comment from a fellow flyer "that thing sounds like a sewing machine"....
I got zero performance increase, it took more work to install, weighs an extra 6oz. and cost an extra $100.00. You can double those figures for a twin.
Like you, initally I'd thought the two cylinder engines fired opposite each other when trying to figure out which sparkplug wire went where as my ZDZ-100NG was my first twin as well. Then it dawned on me that if one considers the nature of two strokes and the common intake system for both cylinders, it can't be any other way.
I put the ZDZ-100 on a Hangar 9 33% Edge (the one in my avitar) and a buddy has the same model with the DA-100. The DA spins the same prop at a bit higher RPM but it is well broke in while mine's only got about 4 gallons through it. But between the the NiMH batteries he's using and the DA, his is 2lbs. heavier than mine. The performance on both models is spectacular and you'd be hard pressed to tell any difference on uplines, but mine fly's a bit lighter....
