Sorry, yes the exhaust headers (always thought that was an American term). Please bear with me, I'm coming from a Honda background so assumed terms were similar.
So the plenum and upper plenum are two different things then? I've seen pics with a plenum space where they remove the top of the engine plate.
DE = single intake, HR = twin intakes.
If you're looking to go down the power route just a performance filter in the OEM airbox will give best results once mapped. Things like pop chargers, CAI etc are more for show and noise, and can suffer from power loss, heat soak or in the(rare, but can happen) case of long tube intakes (e.g. mounted behind lower bumper) water being taken into the engine leading to bigger problems
Oh the dreaded hydro lock malarky, yeah that was a sore subject in the Honda Integra scene, I personally never had an issue for 4 years, I just purposely avoided huge puddles etc as the AEM CAI sat next the driver side wheel arch!
Are there longer versions of the induction kit, I do like noise hence if I can get a long arm variant or even have (if they do them) GruppeM versions for the 350Z.