Foxy Boxing

Foxy Boxing

UPS and FedEx will probably agree with us when we say that boxes can definitely be foxy. We’ve just finished making one such example.

Before we get ahead of ourselves, let’s point out the fact that this box started out life as a CSL-style carbon fiber airbox. The website stated that “some modification” would be necessary for fitment. As you saw with our Smurf Pants attempt, “some modification” should be re-worded to say, “This airbox points directly at the Z4M’s firewall. Good luck now that you’ve purchased it, since we don’t offer returns on it! Nana-nana boo-boo.” As we mentioned, Smurf Pants was unable to work to the degree that we desired, and after a couple other attempts to get it to work, we realized we had it all wrong. The box needed to work for us, not us for it. We have all the materials here to create a new end for the box, one that will greatly simplify the whole airbox setup, so we should do it. And so we did. First, we cut away the part of the box that needed modification, and set about building an aluminum skeleton off which to base the new piece. Before you ask, yes, the airbox piece that’s already created was designed to work with the plenum exactly as we planned to modify it.


From there, instead of spending egregious amounts of hours trying to contour MORE aluminum to fit perfectly around the skeleton, we chose to use thin strips of metal in conjunction with fiberglass to build the rest of the base shape for the box. After the fiberglass dried, we trimmed the excess and had ourselves a skeleton.


We followed that up with some additional fiberglass to strengthen the glass-only portions a bit and provide a better surface to later cover up, then applied everybody’s favorite cake frosting. Mixing up this cake frosting with the frosting on the V-day cupcakes we had yesterday could have disastrous consequences; thankfully robin’s-egg blue is not a typical color associated with the holiday of love.


And then we applied the carbon-fiber overlay with our genuine carbon-fiber. We did this at the same time as the other CF overlay, so you can tell that this has definitely been a work in progress. A labor of love, if you will. But that term was better suited for yesterday’s post.


We had planned for the CF overlay to match that of the airbox as it was purchased. However, during the course of plotting out the overlay, we came to a very interesting finding. What had been marketed as a carbon airbox is actually a black fiberglass airbox. Black fiberglass is basically fiberglass that’s been dyed black, and is a low-cost alternative to carbon-fiber, because the two are difficult to tell apart unless you have experience working with both, which we do. So we came to an executive decision — once the airbox was back together, we’d do another overlay and have it entirely uniform and matching the top half of the filter portion of the airbox. So we fused together the halves of the airbox, forgot to take pictures, and went about using additional filler to ensure a smooth surface for the primer that was to be applied next.


After the primer, we shot it with another coat of black, ensured it was smooth, and did an overlay of the entire plenum top. Once that was finished, we went about the fun parts involving more sanding and painting, which we’ll just gloss over here to get to the good part.


And now we start the fun parts. All that remained after more sanding, painting and polishing was the clearcoat. Which, well, gives away the whole look of it, so we’ll just put all the pictures together. Now this box contains more carbon fiber than black fiberglass, and is definitely much stronger than the original design (this one shouldn’t flex like paper in a breeze under heavy-throttle conditions), and in our opinion, looks a hell of a lot better as well. We added a FMU logo mask in the black paint up top, so that it comes out in carbon fiber, for that extra little bit of flair we tend to revel in. It’s currently taking up residence in the Z4M’s engine bay, where it will soon be joined by the other part of the airbox assembly, as well as the VAC-modified oil pump. After that, it’s off to the dyno and then off to Seattle in time for the nice weather!


See you tomorrow!

  • Alex
    Posted at 16:00h, 15 February

    I have my own CF Airbox produced by a well known company and composites company. I heard most CF Airboxes don’t fit Z4Ms.

    Looking at what you guys did to make this fit is pretty cool! Nice work.

  • fluidmotorunion
    Posted at 16:20h, 15 February

    As they shouldn’t. The E46 M3 and Z4M, even though they share the same motor, are NOT based on the same body and as a result don’t really mate up well for parts that require engine bay space. Some things may be specifically built to tackle both applications, but often times are not. And the company we talked to about this box wouldn’t even begin to give us a specific on what needed to be done for modification. We tried the best we could with building additional pieces to complement the airbox as it stood, but in the end we weren’t happy with how well it was working, so we went to the next step that would guarantee proper filter and MAF placement, along with a flow that’s less restrictive than the OEM airbox.

  • Colin
    Posted at 18:38h, 15 February

    That looks soooooo nice!

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