Originally Posted by Cosworth

Every JDM cat-back exhaust system (except 1 or 2 straight through and under-the-axle design) will have small bottlenecks in the b-pipe. Why? Maybe it's to produce a desirable flow characteristic which can't be achieved by having a straight pipe design. Possibly, bottleneck is good for throttle response and/or midrange gains.

All in all, I wouldn't chop up Mugen exhaust to eliminate the bottle-neck. Mugen knows what they are doing... it's not there for aesthetic reasons.