The open type intakes were made for the HUMVEE engines specificlly. There are designed much lower profile so the the hood on vechicle will close. As to HP, I don't think that this designe would add much HP as ONLY "AIR" goes through this (NOT FUEL). It might help a little to smooth up the intake ports but should help more on the "exhaust" ports.
Remember as to HP, you can take off this alum intake , divided or open type and STILL CRANK & RUN the engine. It would run good of course but will still run. So here again the intake design is mainly the lower profile to clear hood space on the Humvees. I could be wrong--just my guess.