Just think about it: the exhaust port closest to the muffler is blowing out to the other side of the tube creating turbulant air flow - and tho each preceding cylinders before it are doing the same, the preceding cylinders who's gases are trying to escape are running in to each other. To me, its extremely inefficient.
I still think individual exhaust port tubes flowing down into a single collector down at the exhaust pipe is still the most efficient way to eliminate exhaust.
Actually they may very well increase torque in that narrow band, which could help with towing, they will not help higher rpm h.p. though and probably will hurt above 4000rpm or so. They are very similar to the old jet boat manifolds of the 1970's, good for torque below 4000 bad for high rpm h.p.
Just got off the phone with gibson tech support. Said they have been working on them for 7 months and on a stock 04 hemi, 8 hp 30tq. He said on the dyno, he was dissapointed with the hp numbers but was extremely pleased and could not believe the tq numbers. I asked him if he was running a programmer when they did the dyno numbers and he said absolutely not. I guess I have to take his word even though I am extremely skeptical. Who Knows, If it produced half of the tq it may be worth it.