"In this Special Series, I document my CSL airbox experiences. I take you into my unboxing of my various airboxes, the hardware checklist, the tuning dilemma, installation notes and my driving impressions with proper sound clips.

In this entry, I unbox my 3rd, and final CSL airbox: the Karbonius 1:1 replica and its carbon snorkel. I highlight the little things that set the Spaniards apart." 
- Matt

The switch. 

I have previously documented 2x CSL airboxes from HaimusRacing, their premium "frozen" variant and their Shadowline variant. The CSL airboxes they make is great, and their ABS printed snorkel remains what I feel is the best option: it's cheap and pragmatic considering. 

Since early 2024, I have focused on growing EuroConnex into a sustainable business. I chose to divest from the brand over irreconcilable differences on delays and sustained quality across various product development projects. 

I sold the Shadowline airbox, and moved on to my 3rd and probably final airbox: the Karbonius 1:1 CSL replica. 

The best. 

Karbonius Composites got on BMW M owners' radar with this specific product in the early 2010s. For over a decade, they have been continuously improving and refining their manufacturing techniques of the airbox. 

There are minute differences on the exterior that would only be spotted doing an A/B comparaison against the original BMW M product. Short of an OEM airbox, this is the best CSL airbox on the market.

Cured in autoclave. 

Karbonius is one of few carbon manufacturers using an autoclave to cure its carbon.

The process has freshly laid carbon parts and their molds cycled under pressure up to 8x times the atmospheric pressure up to 180C for several hours. The process creates the strongest, lightest carbon, eliminating air voids in the process. 

It's a step up in manufacturing process compared to HaimusRacing as they use pre-preg out-of-the-autoclave (OOA). 

The laid carbon remains pre-impregnated, the core difference resides in the curing process. OOA allows the use of a commercial oven able to reach 100C. It is cured at atmospheric pressure of 1 bar. 

It's a cost effective method to produce carbon components without the capital investments an autoclave requires. It also reduces mold creation cost to sustain the autoclave process. 

I received my airbox in late April '24. 

I opted for 2x2 weave finish in high gloss clear coat, like the original CSL airbox.

The weave alignment is perfect, matching the OEM 3 o'clock orientation when installed. They opted for black hardware instead of raw metal to connect the two sections together. 

All machined aluminum ITB fittings are anodized in black, like the original airbox. 

The underside fittings are also all anodized in black. The original airbox had the center bracket in raw aluminum. 

The IAT bung is located in the original position. 

The underside of the inlet section features the connecting hole for the flap mechanism of the original airbox. 

The weave alignement between sections is paid careful attention during the manufacturing process. 

These brackets are at the rear of the box and meant to support hoses running across the firewall. The Haimus' brackets weren't up to the task and broke off. 

The carbon trumpets. 

Karbonius revised the interior design by smoothening the carbon for improved flow, along with changing the angle of the 5th and 6th cylinder trumpet. They are little improvements to airflow that do generate some performance gains. 

They retained the original design's carbon strengthening beams. 

The trumpet's bell-mouth shape is critical to performance. 

The snorkel. 

The snorkel mimics the original design, without the flap mechanism. The openings and shapes are very similar. 

The triangular inlet is designed to fit with the CSL bumper inlet tube that is connected to the bumper's signature driver side duct.   

The weave is perfectly positioned parallel to the mounting bracket, creating an appealing visual effect when bolted to the airbox. 

Black hardware is included for a seamless look. 

Stepping back from the assembled airbox and snorkel, you grasp the decade long refinements that went into making this the best CSL airbox on the market. 

Art is often described as the compounding effects of many, many little things. The Karbonius CSL airbox fits that description unlike any other I have seen in person. 

The airbox and snorkel will be fitted in the Summer using its specific installation kit using Genuine BMW parts.

Up next: I document the installation and go for a drive.   

Later on in the Summer, I will hit the dyno for figures of the airbox in pairing with the S54-EVO package.