So You Are Interested in a CSL Airbox!
This guide intends to provide high-level information regarding retrofitting a CSL style airbox, to a non-CSL M3. It is possible this guide will frustrate those well versed in CSL airbox installs. The target audience are those interested in learning more or looking for tips how to get the desired outcome. When searching the Web for information on CSL airbox installs, the more you search, the more confusing things can get. This guide attempts to bring key information together using plain English.
….it is not intended to provide step-by-step airbox installation instructions.
Although focused on the E46 M3 platform, some of this information may be useful for similar installs to other models of BMW.
Links to parts and OEM part numbers have been included in the Parts Summary section.
BMW have stopped supplying some CSL parts already (e.g. airbox shut off valve, dipstick guide tube) and may stop supplying others listed in this guide in the future. Information provided was accurate at the time of writing.
The S54 motor is a beauty and must be loved, cherished and respected. Only attempt modifications described in this guide if you have the required knowledge, skills and tools. None of what is described in this guide is particularly difficult, but ignorance and / or carelessness, can result in harm to the motor and electronics. If in doubt, our advice would be to talk to a trusted, specialist garage or installer.
Once the decision to install a CSL airbox has been made, the most important next step is to decide which route to take. More on that later.
Why Install a CSL Airbox?
Noise - no more explanation required.
Appearance - although hidden away, CSL airboxes look the part – we don’t get tired of looking at them.
Performance - shan’t comment on figures, some claim more than others. Our advice would be to set expectations at the lower numbers then any extra will be a bonus. Certainly, a quality airbox, installed correctly, will add a useful dose of HP.
Genuine CSLs are rare and valuable. Non-CSL M3s, especially nice ones, are getting rarer which pushes up their value. Regardless, converting a non-CSL M3 is a more accessible and cost-effective way of ending up with a similar outcome – albeit not a real CSL of course!
Retrofitting a CSL airbox to a non-CSL car is reversible. If, in the future, the decision is made to change back to original, CSL airboxes can be popular secondhand purchases. So, reselling to recoup some money is possible.
Background Information
The factory BMW E46 M3 uses a mass air flow (MAF) sensor integrated into the intake plumbing, prior to the throttle bodies, to calculate the amount of incoming air (Oxygen) to the engine. Retrofitting a genuine or high-quality aftermarket CSL carbon fibre airbox typically removes the MAF sensor assembly completely.
The CSL inlet tract was designed to optimise flow however MAF sensors tend to be placed in a narrow cross-sectional tube to help stabilise air flow direction and minimise turbulence to obtain more accurate measurements. For these reasons, as well as emissions, and perhaps others, BMW chose manifold absolute pressure (MAP) and inlet air temperature (IAT) sensors to measure incoming air mass on the E46 M3 CSL.
BMW refers to the electronics used to control the engine as digital motor electronics (DME). This guide will use BMW’s terminology, DME, rather than more industry generic terms, like engine control unit (ECU) or engine management unit (EMU).
To calculate engine load, correct air fuel ratio (AFR) and ignition timing, the DME uses multiple sources of information including throttle position, engine speed, inlet manifold pressure, inlet air temperature, pre-ignition / detonation and exhaust gases.
Parts Required
To help determine parts required to retrofit a CSL airbox depends on the answers to the following key questions:
Key Question 1:
Do you want this install to be as OEM as possible? If yes, there are a few things to consider. How OEM would you like it to be?
CSL Air Rail - The CSL air rail is different from the non-CSL. The CSL air rail has an additional interface for the new MAP sensor. Although still available from BMW, CSL air rails are quite expensive (~£400+).
CSL Flap - The OEM CSL flap mechanism is used by the DME to reduce induction noise at lower engine speed and alter which ducting the snorkel draws air from. If so, you will need to buy the control unit and flap assembly plus several ducting parts like the intake tube, air duct, suction tube, etc.
Genuine Airbox - Although it is possible to buy a genuine BMW airbox assembly, they are ~£4,000 - 5,000 plus. If not genuine BMW, then which aftermarket solution?
CSL Dipstick - BMW no longer supply the CSL engine oil dipstick guide tube. The CSL part is much shorter than the non-CSL and requires the airbox air filter cover to be removed to check engine oil level – some see this as a faf, others want to be as OEM as possible. The alternative is to carefully bend the existing, non-CSL guide tube so that it routes around the CSL airbox. This modification works well, allows engine oil level to be checked without removing the airbox cover and isn’t particularly difficult - but isn’t ‘OEM’.
Note: MS Motorsport are looking at having CSL dipstick guide tubes remade but these aren’t available yet.
Key Question 2:
Is this a DIY project or specialist garage? If DIY, then you can make all the decisions - within the bounds of not making choices that may damage that quite rare, getting rarer, S54 engine. If specialist garage, then get them to advise on the kit list as per their preferred installation method (i.e. Alpha-N or CSL MAP).
Key Question 3:
Alpha-N or CSL MAP? These options are discussed ln more detail later.
Alpha-N recalculates engine fuel maps parameters primarily derived from engine RPM and throttle position sensor (TPS).
CSL MAP upgrades the stock DME firmware binary file directly to the genuine CSL operating system via a new physical MAP sensor.
Note: Depending on the condition of the car other parts may be required. It is impossible to determine this without seeing the car. The performance of the installed CSL airbox may be limited by the condition of the engine, engine ancillaries, electronics, wiring, etc. It may be required to replace parts not mentioned in this guide.
Karbonius Airboxes
There are several high quality, aftermarket airbox options on the market. Our choice at MS Motorsport, is to supply products from Karbonius (https://karbonius.com/).
Karbonius have mastered the art, craft, science and engineering required to produce top quality parts made using carbon fibre reinforced plastic (CFRP). Making
CFRP parts to this standard, takes significant skill, investment and ongoing monitoring and quality control. Karbonius have been nailing coverage for classic models for years and continue to release products for newer series, including G.
The ‘CSL’ airbox options available from Karbonius are:
CSL Style
This most closely replicates the BMW original part. It is possible with this airbox to run the following configurations:
CSL Style Option 1a - CSL airbox on its own. it is possible to add CSL style option 1b or 1c later.
CSL Style Option 1b - CSL airbox plus aftermarket snorkel (no CSL flap).
CSL Style Option 1c - CSL airbox plus OEM snorkel / CSL flap and OEM inlet ducting.
Race Style
Although very similar to CSL, the Race airbox style has an integrated snorkel section and doesn’t allow for any CSL flap parts to be used.
Both Karbonius CSL and Race styles are available in 1x1 and 2x2 carbon fabric weave patterns as well as gloss or matt finishes. The OEM CSL airbox came in 2x2 gloss.
Air Filters
Karbonius E46 CSL and Race style airboxes use the OEM air filter element design. Alternatives are available. We often supply high-quality filters from ITG. These ITG filters fit perfectly, can be cleaned, re-oiled and re-used. MS Motorsport can supply cleaning kits that include the cleaning fluid and oil.
MS Motorsport can supply the CSL airbox and other parts, including original BMW, required for the installation. See the Parts Summary section for more detail.
Aplpha-N Vs CSL MAP
Standard map?
Firstly, you should never run an E46 M3 CSL airbox on a completely standard, unmodified stock DME map because the CSL airbox removes the factory MAF sensor that the DME uses to calculate air fuel ratio (AFR).
Why not?
No MAF sensor: Installing a CSL airbox requires the factory MAF housing to be completely removed.
Unmetered air: Without a MAF signal connected and measuring actual airflow into the engine, the stock computer cannot calculate proper fuel delivery.
What happens if I try to run a non-CSL map?
Severe running issues: The engine will idle poorly, hesitate, or stall because it lacks correct fuel and timing adjustments.
Limp mode / fault codes: The DME will throw check engine lights and error codes for a missing MAF sensor.
Note: There is mentioned on the Internet of the "Tucked MAF" trick which leaves the original MAF sensor plugged in and zip-tied in the engine bay to try and fool the DME.
MS Motorsport does not recommend this approach. Instead, one of the following options should be used. We describe later some of the Pros and Cons of Alpha-N Vs CSL MAP however these discussions can become religious. Supporters in one camp try to convince those in the other, that their way is best. MS Motorsport has supplied airboxes for both Alpha-N and CSL MAP install and, providing they are installed using quality parts by a competent person, both can provide OEM like drivability.
MS Motorsport doesn’t really have a preferred install approach – it depends!
Note: If you read about Alpha-N online, you will likely hear stories about poor engine responsiveness, hesitations at lower RPM, etc. The latest Alpha-N maps have sorted these issues and we know of several specialist garages and tuners that use this method with excellent outcomes and OEM-like engine responsiveness, pick-up and performance.
Choosing between an Alpha-N and CSL MAP is probably the most important decision when installing an E46 M3 CSL carbon airbox. The primary difference is how they calculate engine load. Alpha-N calculates load based on Throttle Position (Alpha) and Engine Speed (N) – with intake air temperature (IAT) correction. A CSL MAP conversion reads actual intake vacuum pressure using the added physical MAP sensor - mimicking exactly how BMW engineered the factory M3 CSL.
Alpha-N, what is it?
Alpha-N was used by BMW on E46 M3 CSLs as a ‘limp mode’ feature in case of, for example, MAP sensor failure. ‘Alpha’ refers to throttle position (%) and ‘N’ refers to engine speed / revolutions per minute (RPM). This mode doesn’t rely on any MAP sensor input. Installers and tuners have used the Alpha-N option to create a map using throttle position and engine speed. The IAT sensor allows for air temperature ‘correction’ to be included in the Alpha-N tune.
Alpha-N Pros:
Can provide superior performance in optimal conditions using a custom tune.
Simple installation, no other DME modifications are required other than the tune.
Compatibility, can be flashed onto any model year S54 engine, including early 2001–2002 M3s equipped with the non-HP MSS54 DME.
Alpha-N Cons:
DME tune cannot factor in variables such as inlet manifold pressure.
Inability to adapt if conditions aren’t ‘optimal’.
Additional cost of tuning / dyno time.
CSL MAP, what is it?
This is the genuine factory method engineered by BMW M for the E46 M3 CSL. It incorporates a MAP to actively monitor vacuum levels directly inside the intake tract. The DME runs authentic CSL coding to calculate air volume in real-time.
CSL MAP Pros:
Drivability: Similar / same as OEM drivability because the DME has ability to calculate real time engine flow via the MAP sensor and then make adjustments for variable conditions based on manifold pressure and air temperature.
No custom tune is necessary although this is an option with your tuner based on other modifications
Dynamic Adjustments: The MAP sensor reading combines with your air temp sensor to calculate air density. The fuel mixture is corrected regardless of atmospheric conditions, elevation shifts, etc.
Adapt to modifications: The system can tolerate minor modifications to the engine more dynamically than Alpha-N setups.
CSL MAP Cons:
Requires conversion of your DME to the CSL DME configuration.
MUST have the MSS54HP DME or upgraded MSS54 DME, some additional wiring and installation of the CSL MAP / IAT sensors to the DME.
Requires the CSL air rail, or a suitable air
rail modification to the stock air rail, or in-line ‘tap’ added, for the CSL MAP sensor.
Alpha-N Vs CSL MAP Comparison
Load Measurement
Aplha-N - Hardcoded lookup tables based on Throttle Position % + RPM.
CSL MAP - Real-time tracking of Manifold Pressure (Vacuum) + RPM.
Hardware Required
Aplha-N - Only an external IAT sensor.
CSL MAP - MAP sensor, IAT sensor, and custom wiring harness.
DME Requirement
Aplha-N - Works on standard MSS54 or MSS54HP DMEs.
CSL MAP - Requires an MSS54HP variant (or an upgraded / cloned unit). If running the CSL flap then the H-bridge motor controller hardware needs to be added.
Altitude Adaptation
Aplha-N - Poor. It cannot sense changes in environmental atmospheric pressure.
CSL MAP - Excellent. Automatically adjusts fueling during significant elevation change.
Installation Effort
Aplha-N - Minimal. Plug-and-play after basic IAT wiring. Dyno time recommended.
CSL MAP - Moderate. Requires pinning wires directly into the main engine DME connector.
SMG Vs Manual
Airbox to Throttle Bodies
TBC
Parts Summary
This section provides a summary of parts typically required for a CSL airbox installation. As mentioned previously, the parts list depends on the model, year, current state of the car, SMG or manual and the various airbox installation options. It is intended that this section is used in conjunction with previous sections that describe the options. Previous sections describe how you may like to complete the install, this section hopefully points you to what parts you may need for your specific install.
Parts marked with a * are no longer available (NLA) from BMW.
Airbox Parts
CSL airbox OEM [11617833496]
CSL snorkel / flap OEM / ducting [11617833498] [11617833648] [11617833646] [11617833645]
Air filter OEM [13727838625]
CSL air rail [13417833597]
non-CSL air rail [13547831481]
* CSL engine oil dipstick guide tube [11437833653]
non-CSL engine oil dipstick guide tube [11437832140]
| Part | OEM Part Number | Aftermarket |
|---|---|---|
| CSL airbox | 11617833496 | Race Airbox sjdhcbsjdj jshbc jshbc jshcb jshcb |
| Row 2, Col 1 |
First Second Third |
Row 2, Col 3 |
| Race Airbox | Row 3, Col 2 | Row 3, Col 3 |
| Row 4, Col 1 | Row 4, Col 2 | Row 4, Col 3 |
Tools Required
CSL airbox installation requires standard tools. One recommendation would be to get specialist pliers to help install the low profile, ITB-to-hose and airbox-to-hose clamps. The specific pliers required depend on the clamps being used. It is possible to use normal pliers (e.g. long nose) but the specialist versions can help ensure an effective seal and can help with the limited space available.
Helpful Tips
Once the airbox is removed, the individual throttle bodies / intake plenums provide an excellent slide for small objects to gain entry into
the engine. When bare, it is wise to cover these ‘death slides’ to prevent a few hours’ job turning into a few days’ job.
Disconnect the battery before working on an airbox installation.
Be careful when working with carbon fibre products as they don’t respond well to overtightening fasteners or fixings. The carbon fibre and resin matrix is very strong but doesn’t like excessive compressive loads caused by overtightening fasteners. Once crushed the carbon fibre is useless and will require repair or replacement.
After installation, make sure the throttle mechanism works correctly and doesn’t bind when opening or closing. For example, the airbox to inlet runner hose clips.
Some electrical wiring changes are required but, depending on the installation options chosen, these aren’t particularly difficult. We would estimate this as an intermediate skill level task (e.g. pin swapping & harness adaptation). The trickiest task is probably adding the signal and ground wires into the standard DME connector for the new air temperature / IAT and pressure / MAP sensors – but even this isn’t very difficult for anyone who has a little experience of automotive wiring and how automotive electrical connectors work (e.g. inserting a new pin into the existing DME connector).
There are many very helpful and detailed blogs / vlogs that show the installation process for most of the options discussed in this guide.
If you have SMG, then recommend having the SMG software updated to CSL to match upgraded inlet system and CSL engine management.
Final comment: Our advice is to start with the desired outcome and work backwards. If getting a specialist garage to perform the install, they will have their own preferred install method. Buy the parts required to perform the install as per their preferences and advice.
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