Look at the engine bay of the zed and think about it in a prototype process.
Generally speaking most automotive companies follow a process where by your prototypes run in the manner of:
Powertrain & chassis prototypes, these are normally hidden under a previous models body as they are mostly cut and shut jobs to shoe horn it in for testing purposes as these departments need mroe time in developement.
Body prototypes, these advance on the engine prototypes, depending on the level of change sometimes they are still in a previous cars body and sometimes all wrapped up in camo as they resemble the finished shape. these also aim to have alot more functionality within the rest of the vehicle as they are a test bed for most depts.
Production intent prototypes, these are meant to be exactly what will be produced but made in a "one off" manner.
Manufactuing prototypes, used to develop the manufacturing processes.
this is the fundamental way companies work and is no secret.
So, back to the zed engine bay...
The engine is designed for the car on test beds, then they are put into the chassis and developed from there in the first prototypes, at this stage the car is very immature and it is difficult to complete accurate tests on its driveability.
As the car moves through its prototype stages nissan may have found the front end of the car needing a stiffen up. by this time the engine is designed and already in the car, it cant be moved, the plenum is already designed and being used. So how do we fit a strut bar in...
the options available:
-Place above the exsiting plenum, this requires a raising of the bonnet as there is a specified gap by law between any solid under bonnet parts and the bonnet itself for pedestrian impact purposes.
-Lower the front of the plenum, this slightly starves the front two cylinders of air but allows the required clearences to fit the bar in without an alteration of the bonnet.
Which one is cheaper and which one will nissan choose?
Thats right, they starve the front two cylinders as its cheaper than all the other available options.
And so the plenum spacer is a polular mod in the 350z