Dual-Model Muffler with Variable Back-Pressure Valve

I saw this on the Mitsubishi website and it had me scratching my head. Anybody know exactly what it means. I searched these forums but only found one thread that seemed to address it. The explanation was still sorta vague though...

Variable back pressure

 

Inside the muffler there is a flap, at idle and low rpm's it is closed to raise back-pressure which is meant to increase low end tourqe. When the exhaust flow increases the flap opens to provide the higher end hoursepower. At least that is the theory behind it.

 

It's always been my understanding that the best exhaust on a turbocharged engine is NO EXHAUST. Doesn't the TC already create sufficient backpressure for that low end grunt.

 

I think that part of it is Mitsubishi propoganda but that little bit more backpressure may help.

 

Think of it as the same idea as an exhaust cutout except on a very very suttle note. Not to mention the added weight.

 

I modified mine a year ago and can detect no difference in low end power. I designed a diverter vane to distribute gas flow and hold the gate open at the same time. The big change I notice is to low freq sound pressure levels. The spring loaded gate creates back pressure at the very end of the system. If you look at the muffler where the entrance pipe is mounted you will see heat discoloration. Heat to transfer to such a small area is an indication to me that gas flow slows at this point. If true, then the slower moving gasses must be pushed out by the faster moving gasses farther back the pipe which is a restriction in my opinion.