Misunderstood Complexity: CSL Airbox

Misunderstood Complexity: CSL Airbox


  1. Backstory to this Connex
  2. First Impressions
  3. Design Details
  4. Let's talk Trumpets
  5. Fast is smooth!
  6. The Snorkel

1. Backstory to this Connex.

I’ve been watching Antonio bring to market his E9X plenum mindfully, explaining every step of the R&D process.

I didn’t immediately reach out when it was released, as I was aware of the history on previous CSL airboxes that had quality issues.

Since then, 50+ carbon plenums were delivered to S65 owners with great reviews. 

I’ve chatted at length with Antonio on the backstory, and found what I believe to be an honest, transparent BMW M enthusiast that made things right.

He put his money where his mouth was and went into debt to cover a massive recall campaign, and become sole owner of the business. 

It was back to the drawing board to revise the trumpet fixation design.

Over 150+ CSL airboxes have been delivered since. 

Just like my E9X CarboProject plenum, matt finish is where it’s at on engine components. 

I convinced Antonio to develop a matte "Frozen" finish for the S54 CSL Airboxes. I finally received it earlier in January 2022. 

2. First Impressions.

HaimusRacing packed this for a trip to the moon, I'm glad they did. 

The Bulgaria to Canada connection took 4 business days via UPS - and the box came in perfect condition.

What I immediately noticed is the matte finish and the optional Haimus Racing sticker applied under the clear.

I wanted the unique touch of color matched Phoenix Yellow stripes.

Coming from the S65 & S85 plenum, what first hits me about CSL airboxes in the flesh is the higher level of engineering & design requirements.

The Haimus Racing kit has visibly gone through many revisions to ultimately reach this current state of design.

I handled it like jewelry at first - and no lie, this is a piece of engineering & design porn.

I've seen lots of carbon products and it's no secret I'm a big advocate of pre-preg & autoclave carbon.

It's what is used here - for its superior tensile strength & lightweight that allows a thin walled construction for optimal sound.

The 2x2 carbon work is impressive. The weave is optically pleasing and the seams are well done.

I noticed no carbon flaws.

There were a few areas where the clear coat has "popping" - commonly known as pitting, this happens when the 2 component clear coat traps some solvent used in the process in between coats and evaporates through.

This can't be fixed with polishing on a matte finish - but the areas are hidden from view.

My OCD wasn't triggered, and I'm an acknowledged ass when it comes to carbon work & paint.

The kit I opted for comes with the ABS printed snorkel. It's a simple, effective design without the OE flap.

I don't wish this was carbon, but I understand those that want the extra bling.

The snorkel is fitted with bolts & nuts, with a custom made aluminum sleeve to the aluminum ring bonded on the carbon section.


3. Design Details.

Time to dive into design details of the Haimus Racing CSL airbox.

In my research, there are many stories about failing air boxes from various brands causing catastrophic engine failures.

The culprits often come back to failing adhesives on the multiple fittings on and within the airbox.

What matters to me first and foremost is reliability and durability.

This is where Antonio at Haimus has spent a considerable amount of time, money and developed key expertise.

This airbox isn't new - what's new is the frozen finish.

Over 150 have been sold since it has been completely revamped and it's been proven reliable since.

It's backed by a 5 year structural warranty.

Upon careful examination of the airbox, you will find all bolt threads, bungs, alignment pins, snorkel ring, brackets and most importantly the ITB fittings are made from CNC'ed aluminum.

The only non-aluminum brackets are the 2x carbon brackets by the side wall to route hoses.

The trumpets and sensor Bungs are not only adhered with aviation grade adhesive specifically picked to handle the harmonic vibrations the carbon airbox generates on the S54, but are also thread locked with a custom nut on the outside.

Additionally, Antonio deleted the thin carbon support beams from the OEM design as these were a source of failure on other boxes.

The pre-preg carbon used by Haimus is sufficiently rigid to do without these, and eliminate a failure point.

Another interesting design detail is the rubber stripping used at the junction to bolt & unbolt the box for filter replacement.

The rubber stripping makes it *feel* better when installing, but also eliminates vibration issues and reduces probable scratches you'd induce as you service the box.

Lastly, the optional ABS printed snorkel is fitted using a sleeved bolt & nut carefully spec'ed to avoid any scratching issues with the carbon.

A matte finish can't be polished - every bit helps to keep it pristine.

These CSL airboxes are complex - the engineering & design expertise is not only for reliability, but also performance.

I'll touch on the unique trumpet features in the next section & the long list of hardware & software to complete the install.

4. Let's talk trumpets.

While first thought of by many as a musical instrument for the S54, the CSL airbox developed by BMW M was first and foremost a performance product.

The booklet that came with the Haimus Racing CSL airbox was filled with in-depth information and diagrams about what makes this box purposely developed for reliable performance.

First thing first - it's light.

The carbon assembly comes in at around 1,800 grams - or 4x times an (american) football's ball.

The carbon trumpets are "wet riveted" for durability.

In simple terms, the trumpets are slid through the threaded CNC'ed cups with excess adhesives during their assembly.

That excess spills out from holes in the CNC'ed cups to reach the optimal amount required.

A metal ring is then threaded locked to the cup protruding from the airbox.

It creates the metal fittings that slides on the ITBs and rubber hoses.

Still with me? Let's change pace.

5. "Fast is smooth!"

We've heard that one before.

It also applies to airflow.

The insides of the carbon airbox is smoothed out to reduce turbulence, including the signature carbon trumpets of these boxes.

You can visibly notice the curved edges of each trumpets.

Dimensions are changed to enhance the with the stock CSL airbox to slightly augment the radius of the bell curve.

The altered trumpets help create a vacuum effect at 3000 and at 7000 RPM.

Haimus claims they create more midrange power then any OEM CSL replica airbox from 3000 to 7500 rpm.

Trumpets 5 and 6 are placed further back and slightly shorter.

They further claims this allows for direct airflow, bumping up power levels in the mid to top-end of the RPM range

6. The Snorkel

This is a simple, effective design made from 3D printed ABS.

It doesn't re-use the OEM flap and connects with the OEM CSL bumper attachment, or can be fitted with a standard bumper.

Replacing the fog light with ducts could work as well.



  • Matt

    @Andrew, it’s available here: https://euroconnex.co/collections/e46-m3/products/csl-carbon-fiber-airbox

  • Andrew

    Is there anyway to see the price for individual purchase? Thanks in advance.

Leave a comment

Please note, comments must be approved before they are published

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.