I'm not necessarily convinced that these plenums are a good bang for buck upgrade, but I'm always amazed that people say this!?
anyone who has ever worked in an engineering environment knows that in design, there are two considerations
1.) is the design fit for purpose
2.) cost
the notion that nissan spent years pondering the best way to extract small HP improvements and maximum flow from their plenums is just ridiculous. The factory plenum is designed to be as cheap as possible to manufacture, whilst still performing the job adequately for purpose - i.e. low boost road use applications.
it's like saying that they spent a bucketload on r&d for their gts-t intercoolers - because nissan engineers and nissans are good. yet everyone knows that the factory intercoolers have got knobs.
the question for me on the plenum is - can you get it at a cheap enough price to justify the opportunity cost against other mods. i.e., if I spent that (up to) $2500 on something else, could I have acheived a better end result? I'd say no, unless you've done a lot already.
however, if you start talking about $800 instead of $2500......