Pelican has been selling a version of this since the beginning. Apparently, the Manta system doesn't offer any increase in HP, but the idea is not lost on me.
Everything after the merge is junk, IMHO.
I guess they no longer have it in the 911 version. The catalogue confuses me. and, I don't know why the pic doesn't show. I posted this exhaust many times over the years as I had on once on a car I bought. The system was rotted out and not useable, but sounded awesome. Better than anything I've heard yet. too bad it didn't help the HP.