"These build journal entries are part of a Special Series on the development of the S85 CSL Style Carbon Plenum and S85 CSL Competition Complete Carbon Intake System.

In this entry, I document the technical differences of MAF, MAP and Alpha-N engine mapping. I discuss why the S85 was built for AlphaN, the mapping process and I end with my driving impressions drawing a comparaison with the M3 V8."
- Matt

A brief history and definitions. 

Mass Air Flow. 

MAF sensors measure the Flow as a Mass of Air.

MAF sensors are extremely accurate in knowing how much air is entering the intake system, but not only that.

The S85 MAF also includes a thermosensitive element: it monitors air temperatures. This will be useful later on as both alttitude and temperatures determine air density: a fundamental element to making power.  

One of the downsides to MAF are limitations imposed on intake designs: if there are any changes to the overall diameter or shape of the tract on aftermarket intakes, you're going to have error codes for wrong data readings.

The MAF sensors are positioned in the intake trace besides the sealed filters.

OEM filters get dirty leading to MAF sensors needing to be cleaned. 

Mass Air Pressure (MAP). 

MAP takes into consideration the absolute pressure as it accounts for both vacuum (negative) and open throttle or leaks (positive pressure) to deliver its readings to the DME. 

BMW got their feet wet with Mass Air Pressure (MAP) sensors with the S54. 

My CSL airbox uses a MAP sensor conversion over Alpha-N. 

The MAP can't read air temperatures. You also need to refit an IAT sensor to the CSL airbox. 

 

BMW M didn't bother with MAF on the M3 V8.

Using the MSS60 variant, the S65 used MAP and IAT sensors to great effect: the S65 always felt hyper responsive, visceral and ready to jump out of the engine bay. BMW M has been using MAP ever since on their M engines. 

The S65 has the IAT sensor located on the passenger side of the plenum's inlet.

Why was MAF still used on the S85?

Following up to the CSL and its MAP conversion drivability issues, we can speculate that BMW M didn't yet feel confident enough in offering their flagship M5 with a MAP sensor such as the CSL considering their documented hesitation issues. 

We'll never truly know. 

In 2005, MAF derived engine maps were still considered the all encompassing, risk free engine mapping option when the V10 was introduced. Ultimately, BMW M engineered the M5 for its target market: executives looking for an edgy daily driver, without compromises. 

My main criticism of the V10 M5 has always been its actually soft edges. The S85's throttle pedal has always felt like jello even in Sport Plus. I documented this in my blueprint to my build here. 

I picked up my 100% stock M5 in the Summer of 2021: I was sort of the target market, 15 years too late. 

 

Emissions target.

Fitting a V10 to a mass produced 5 series was mad enough - it also had to meet emissions across all weather conditions, and engine maintenance level.

Remember BMW's 15,000 miles / 25,000km oil change recommendations? Poorly maintained S85s are still able to meet emissions requirements by using MAF to adjust its adaptations. 

Alpha N Basics.

Compared to MAF engine mapping, Alpha N is when the throttle position is used as load rather than the air flow readings from the MAF. 

Alpha is the throttle position and N is the engine speed. 

The air-fuel ratio is called lambda number (λ). It determines the mass ratio of air and fuel in the combustion chamber.

The V10s were built with AlphaN in mind.

BMW M left a switch in the code: you can configure AlphaN on the V10 by using the MAF as the temperature sensor in a simple code change. 

The compensating factors for inlet air temperature, barometric pressure, oil temperature, coolant temperature etc are all the same in AlphaN as they are when the MAF is used.

Fuel correction is set to lambda 1.0 for idle and partial load driving. The adjustments are then made extremely rapidly given how powerful the MSSx ECU’s are. 

There is no rewiring needed for IAT sensors: the MAFs are kept. The airflow readings are turned off, and the temperature readings from the thermosensitive elements are used to tune for AlphaN.

 

Why? Moore's law!

Until the MSS65 was introduced, there had never been any other BMW M ECU designed with AlphaN in mind. The MSS60 is claimed to be capable of more than 200 million calculations per second, it exponentially exceeded the S54’s ECU by a factor of 8x.

The MSS54 and MSS54HP found in the E46 M3 could run on Alpha-N as a failsafe mode only. I documented this in my Alpha N v MAP conversion dilemma in the Special Series covering my CSL airbox experience. 

I had to swap a MSS54HP to run the CSL airbox with MAP. It's still just a gameboy in a world of Playstations. 

The AlphaN mapping process. 

The process itself is just like a standard S85 MAF tune: buy a tune, receive the flashing cable and load the software. We use common stage nomenclatures to group upgrades into packaged tunes.

We can also change other variables such as V max removal, increased rev limits, cold start delete, etc. 

 

Cable gets plugged into the OBD2, and the process begins. This picture was while loading a tune on a local member's S65.

Keep your maintenance schedules tight, and consider your emissions tests. 

AlphaN is built for enthusiasts - marketing talk that infers expectations of tight maintenance schedule on oil changes and air filter cleaning & changes if required.

Each jurisdiction will have different emissions testing. AlphaN creates more variability in emissions produced by your engine. As a rule of thumb, the better condition it's in, the less emissions it'll produce. 

So what's the point? 

AlphaN uncovers the raw V10 experience. 

Gone is the jello: there aren't any interferences when pressing the GO pedal. 

It feels as if my right foot was directly connected to the engine: the closest thing to a cable actuated throttle body.

It feels mechanical. It feels like a V10 should.

AlphaN is a must have if you're an enthusiast with a disciplined mind for maintenance.