there are equations that show that the VOLUME of the exhaust is a large positive factor on power, both HP and TOURQUE. [a donny peterson article long ago] the whole idea of dual exhaust on cars, with the crossover, is it increases the volume of the pipe and mufflers - not flow - volume. mufflers and proper back pressure are needed in all cases, on motorcycles the issue revolves around making power with pipe and muffler volume too low. short pipes can be tuned for very high output but much lower low speed torque. [drag pipes are fab at a 100] with a sidecar you don't lean so the clearance issues are not severe, and its already very heavy so pipe wt is not a issue. the highest power you will get is with two large mufflers -the larger the better, with a smallish outlet on the mufflers. essentially fulsac. two into one pipe will be a big drag making a turn in a intersection 3 up.