you know how the 2000-2001 maxima's have 222hp(227 hp in the AE), but still use the same VQ30 motor as the 4th gen(95-99)? they gained the extra hp by adding an intake manifold with dual intake runners which allows more air in on the top end to provide extra power that was lacking from the 4th gen maxima's. in the 4th gen's the power tends to fall off after about 5,000 rpm or so. on the 5th gen's with the Variable intake(VI) they pull hard all the way to redline.
this picture here kind of describes it:
air travels in through passage A alone up to 4000 rpm, then the power valve opens and allows air to travel through passages A&B and let more air flow in to help provied the extra 30 or so hp. there is also a variable muffler on the 5th gens that do the same type of thing. they have dual tips; up to 4000 rpm air is only flowing out of one tip but when the variable intake opens up the second exhaust tip opens as well to let more air out to help provide even more power.
that's why the motor in the 4th gen maxima's is referred to as the VQ30DE and the one in the 5th gens is the VQ30DEK. the k stands for kaizen, which is a japanese term that means better or improvement.