Well it didn’t take long before I started to play with the wagon.
The seller included a bunch of spare/old parts with the car, including this pair of pod/cone filters and pipes to fit them, so of course, since I’m waiting for Mini bits, why not take some time to make the wagon sillier?
The factory airbox on the E9x series 335i cars is known to be quite restrictive, as there is very little volume in the lid for air that has been filtered, to travel to the inlet pipes. The N54 Z4 has the same airbox but with a bigger volume lid, so its common to swap that over, but no one has done a dyno comparison yet. The easiest way to sort the restriction is to just take the whole box out, and fit a Dual Cone Intake (DCI).
This is how the box works. Brown arrows are unfiltered, dirty air coming in from the snorkel. Grey arrows are where the air goes from the bottom of the box, through the filter, into the top of the box. Blue arrow is the filtered air going from the filter side to the inlet side, and the green arrows are the air shooting off into the turbo inlets.
Not much room for air considering how much air must be needed by the turbos when they’re pushing 20psi.
Most twin turbo cars will combine the turbo inlets and run just one filter, but the N54 runs the two completely separately. These normally join together in the standard airbox and draw from the single filter, but with cone filter, it needs one per turbo inlet.
Removing the airbox isn’t too hard, just a bit of a fiddle if you don’t remove the cowling. It can be done though. First use a flat blade screwdriver to pop the three clips holding the cable bar to the cowling at the rear of the engine. These slide towards the front of the car to release the bar
I actually ended up completely removing the snorkel to make my life easier. If you need to, there are two torx screws above the grille on the front
This is the one real pain; undoing the hose clamp at the back of the box. It’s a normal hose clamp, so stick a torch down there and undo it. I had to use an 8mm ratchet to reach mine, but I have aftermarket intake hoses so a long screwdriver may also work
Then remove the front hose clamp, and remove the box. It takes a lot of wiggling to get out, so just be careful of everything around it. There are three grommets that are holding it in place and need to be pushed up to release. There is one at the front, inside the bottom of the box, and two on the rear edge. I found the rear ones were easiest to release if you slip a hand under the box and give it a good push upwards. Do note I have heard that the wires on the passenger’s side of the box are meant to be attached to the box (mine weren’t but its been off before), so check that before ripping the box out. If they are, just push them up to slide it off the mount.
So much room for activities. My filter kit was custom made by the previous owner, so fitting won’t apply to anyone else, but the basic idea is to slip the pipes into the hoses, do the clamps up and then slip the filters on the pipes, do these clamps up and away you go.
I didn’t notice at the time but it bothers me now. I rotated the filters so the logos were the right way up, but the front one now shows the ugly metal join, so I’ll need to rotate that and hide it.
The results? Sucky noises are now present, but not as loud as expected. Whooshy turbo noises are louder and you can hear them more often. Psssshhh noises from the diverter valves can now be heard when letting off the throttle too. Car seems more responsive down low, but I haven’t had a good chance to hoon it yet so the verdict is still out if it’s just for noise or if there are any real power benefits.
It’ll stay on for a while. If the noises bother me or something I can always refit the standard box, it’s no big deal.