I have only worked on one Banshee with a two into one exhaust system and countless number of Banshees with the Trinity one carb into two cylinder intake manifolds.
The air flow from these intake manifolds do not fill the reed cage evenly. There is more flow on the outside of the bend than the flow on the inside of the bend. When this happens it hurts power and usually causes the outside corners of the reed petals on the outside of the bend to fail prematurely. Higher flow on the outside of the bend causes the reed petal to start opening first. When one corner of the petal opens first, that corner tends to make contact with the reed block first when that petal closes.
I have done a lot of testing on the racing jet ski engines that used the two into one and 3 into one exhaust systems. With enough cylinder development and twin carb tuning, we could usually get the engines to produce competitive reliable power with the 2 into 1 exhaust. Two into one exhaust system always favored one cylinder over the other. When one cylinder is favored over the other cylinder, the pipe's scavenging and return pulse causes the favored cylinder to produce more power and the favored cylinder's piston always ran hotter.
On the engines that had single carbs and the two into one exhaust systems we usually could not tune both cylinders to produce max power. If you tuned the single carb so the the weak cylinder could produce max power the favored cylinder would not usually survive.
Two into one exhaust systems that I have worked with usually favored the cylinder whose exhaust gases had to turn the least amount at the bend at the junction at the "Y head pipe" and main pipe body.
