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What the Hell is “Alpha N” Tuning?!

What the Hell is “Alpha N” Tuning?!

Recently a video @legitstreetcars did featured a dyno battle with cars that we had tuned, and it has been raising the question “what is Alpha N”? After rummaging around in various threads on the internet and seeing comments on many different YouTube videos, we decided it would be a good time to give everyone an in-depth explanation as to what Alpha N is, and how it can be used for performance gains. Now those familiar with Fluid MotorUnion know that with the help of HD Tuning have been using something known as “Alpha-N’ Tuning on some of our wildest builds since 2010. This includes our M – roadster, nitrous E46 M3, Our record-setting NA E60 M5, F1 inspired water meth injection E90 M3 and of course, Goldwheels. The question of MAFS -less tuning is again popping up, so we thought we would take a moment to describe the benefits and drawbacks of running the tune this way.

Modern computer-controlled engines use a variety of methods to calculate intake air volume in order to dispense the proper amount of fuel needed to hit the desired target air-fuel ratio. For the sake of simplicity, we will be discussing the BMW E39 M5’s method of air mass measurement. Known as a hot-film air mass sensor or “MAFS”. The ECU sends an electric current through a thin wire located in the intake. This current heats the wire to a constant temperature. As the clean cool air passes through the air intake and circulates past the wire, naturally it has a cooling effect on the hot wire. As the air attempts to cool the wire, the ECU keeps track of the increase in electrical current needed to in order to compensate for the cooling effect. From knowing the change in resistance, the ECU can then calculate the volume of air passing through the intake. The ECU sees this volume and can accurately make changes to the required fuel injection timing.

Having the correct volume of air is important because an engine can be at a given RPM but have a different load demand. Wide-open throttle ascending an incline at high rpm and cruising along at the speed limit have different load demands. What if it’s hot and humid, you are at altitude where the air is thin, or it’s a chilly day and the air is dense? In order for the MS S52 DME to accurately determine fuel injection time for this wide variety of conditions, the engine control module uses the following parameters:

Air Mass
Engine Coolant
Battery Voltage
Catalyst Temp
Barometric Pressure
Oxygen Sensor Feedback
Throttle Position
Engine RPM
Intake air temp

Feedback from all these inputs helps accurately trim fuel for the requested demand. While the sensor for the air volume would seem like the most important input for calculating fuel requirements, there are other inputs and methods used to fine-tune and in the event of a failure. This is where “Alpha-N” comes into play.

Alpha-N is not something that a tuner in the aftermarket has developed. Alpha N mode is often regarded as a built-in default mode for the engine in the event the air mass calculation method is missing. Alpha representing the angle of the throttle plates and N for RPM. The throttle angle is a representation of the driver’s input via the pedal and the computer’s demand on the idle control valve and throttle actuator. RPM is detected by the engine crankshaft sensor. When developing the engine, the engineers have a pretty good idea that for a given engine rpm and throttle angle, the air volume can be relatively estimated, and a predetermined fuel value can be used. This isn’t exactly accurate and was primarily developed as a backup, as there are slight production variances, regional climate conditions or fuel discrepancies between the same make a model. Alpha N takes these idiosyncrasies of your specific car, along with the conditions and manner in which you desire to operate, and optimizes this “default” engine control method.

With Alpha N there is no direct measurement of either the mass of air, nor the volume of air entering the engine. The partial obstruction that is a by-product of using either a MAF sensor or AFM sensor in the intake path is removed. The air can flow right into the engine unobstructed. This was key for us achieving the notorious melody of our open velocity stack builds, as any obstruction on a trumpet changes the sound. Having one less sensor simplifies the system, and lowers the maintenance cost in the event of MAFS failure. Also when heavily modifying a vehicle where the airflow is drastically different than the OEM configuration, the MAFS for your vehicle can be at its airflow calculation limit, meaning more air is moving past than the computer can account for. So going Alpha N might be a good option when simplicity and cost are an important factor in a performance build.


There are drawbacks, however. Now if you have an Alpha-N system, and add a large-bore throttle body that allows more air into the engine, but you do not recalibrate the Alpha-N table, then the computer has no knowledge of the added air volume entering the engine. The fuel injection time that was appropriate for smaller throttles is still what the engine thinks is in place. Having the wrong mixture is troublesome, and if it runs too lean you can potentially damage the engine.

That is why folks say that an Alpha-N system needs to be recalibrated whenever a change to the engine is made. Even though the DME still has air temperature, barometric pressure, engine temp sensors to try to compensate for density changes in the air due to temperature and elevation, the estimations relied on data imputed into the alpha n table by the tuner. This is why using a Dyno with a wideband air fuel sensor and logging various engine parameters is the best method to employ an “alpha N” tune. So if you take some time for your tuner to set the Alpha N mode specifically for the mods on your vehicle, you can end up with an engine load calculation method that can rival an air mass meter in power and response.

So can you just pull your MAFS sensor connector wires and run your car disconnected? Well, for testing purposes as seen in the video, you could. However this will lead to a check engine light, and the default alpha n table used by BMW isn’t the most accurate for performance. The Bosch style MAFS used on the E39 also has the intake air temp sensor incorporated, and this input can be used for determining spark advance and also trim fueling. So without proper modifications made, you have one less input for helping the engine perform optimally. Ideally, an “Alpha N” tune like one used by Fluid MotorUnion will not only delete any faults triggered by the disconnection of the MAFS, but will also optimize these tables for peak performance in accordance with your specific engine modifications. The intake air temperature sensor will also be suggested to be relocated to the optimal position for your application. Ideally, we recommend running with proper functioning MAFS on every possible application. In the case of S54, S62 and the S85 there is noticeable throttle lag at tip-in, which for marketing purposes has been labeled as “more linear throttle.” Healthy, properly sized MAFS maximize power and fuel economy until you reach a point where you run open stacks, custom intake, or supercharger where the MAFS become a hindrance.

If you are searching for more information on Alpha N tuning then Fluid MotorUnion can Help. For the past 10 years, we have built some of the wildest naturally aspirated BMW Alpha N cars and are familiar with the challenges associated when it comes to making the most power. We are partnered exclusively with HD Tuning so if you want the simplicity and response that an Alpha N tune can provide, then the experts at Fluid MotorUnion in Naperville IL have got you covered. You can get in touch with us by calling (630)305-3054 or emailing Blog@fluidmotorunion.com. Or stop by our shop located just off I88 next to TopGolf in Naperville.

Here are a few links to youtube videos of cars we have run Alpha N tunes on.

N/A E60 M5
E46 BMW M3

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