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Smart Tuner SMT6 - Airmass Meter Adaptation Application | Application Note : AN 3.7



Perfect Power Application Notes.


Application Note : AN 3.7

This note describes ways to adapt different airflow (air mass meters) to a stock ECU via a SMART TUNER SMT5 or SMT6.



The airflow in to an engine has to be metered so that the ECU can supply the correct fuel. Very often the stock-metering device is no good, too small, or too expensive, and it must be replaced with a different unit, which leads to all kind of problems. The following different air flow meters exist :

Analog Output Hot Wire System

The air flows over a heated wire and cools it. The amount of cooling is proportional to the airflow, and the output is a "DC VOLTAGE" describing the amount of air. This unit is also called an AIR MASS ENTER, because it recognizes the air density.


 SMT6 Piggy-Back Unit - Analog Output Hot Wire System



Frequency Output Hot Wire System

Same as above, but the output is a frequency, which describes the amount of airflow. This device is also called an AIR MASS METER!
SMT6 Piggy-Back Unit - Frequency Output Hot Wire System



Analog Output Mechanical Door System

A trap door is placed in the air stream, and the flowing air opens the door against a spring. The degree of door movement is measured via a potentiometer and results in an analog output voltage, which is proportional to the airflow. This system relies on the spring tension and mechanical "DAMPENING", because it OVER SWINGS at acceleration.
SMT6 Piggy-Back Unit - Analog Output Mechanical Door System



Absolute Manifold Pressure Sensor (Map, or Amp)

This device measures the manifold pressure after the butterfly. Its output is an analog voltage. It is not directly a measurement of the airflow, but indirect the engine load can be determined from it, and the ECU can adjust the fuel accordingly.
SMT6 Piggy-Back Unit - Absolute Manifold Pressure Sensor (MAP, AMP)




If your ECU requires an ANALOG airflow signal, then you need an ANALOG airflow meter. NOT the same make, but analog!
SMT6 Piggy-Back Unit - Restrictions
If your ECU requires a DIGITAL (FREQUENCY) airflow signal, then you can replace the existing metering device with a frequency meter ONLY.


The SMT (5 or 6) can handle analog signals (every mode) and frequency signals in mode 10 only.
Mode 10 : Single Ignition retard/advance + FREQUENCY
The SMART TUNER cannot convert an analog signal to a digital (frequency) one, or a digital signal to an analog one. (These features may be added later).
The analog-to-analog adaptation or frequency-to-frequency adaptation is a standard feature of the SMART TUNER range.
The signal adaptation is done via the analog map. Following is the DOS screen of the SMT6 software.
SMT6 Piggy-Back Unit - Airmass Meter Adaptation - SMT6 Software Screen
Each map point (128) can be programmed with a value from -99 to 126.
A ZERO map value : The output equals the input
A POSITIVE map value : The output is HIGHER than the input
A NEGATIVE map value : The output is LOWER than the input
The map points are SELECTED by a cursor, which is moved via two SMT6 inputs :
ANALOG DEFLECTION : Moves cursor left to right (horizontal)
Normally the throttle signal.
RPM DEFLECTION : Moves the cursor up and down (vertical)
Comes from the RPM IGN1IN signal.
For a straight adaptation, the analog deflection can be grounded and the following map will suffice :
SMT6 Piggy-Back Unit - Analog Deflection Map
The numbers in the first column are the values, which change the input voltage to produce a different output voltage at the indicated RPM. The numbers itself are arbitrary, they just demonstrate that at 600 RPM the output is LOWER than the input. The important thing is that the signal is tuned by the RPM, which is not necessary the right thing.
If the analog deflection input is connected to the throttle, then the following map may be useful :
SMT6 Piggy-Back Unit - Analog Deflection via Throttle
This map lowers the output at 600 RPM closed throttle, but increases the output as the throttle is opened. The signal is RPM and THROTTLE tuned. Again the numbers are arbitrary, just demonstrating the principle.
The next variation is only possible with an ANALOG input signal from the air-metering device. If the analog deflection input is connected to the input signal then the map may look like :
SMT6 Piggy-Back Unit - Analog Deflection is Airflow Signal
Again, at very little airflow the output is lower than the input, and at high airflow the output is higher than the input. This map is deflection tuned, because the change in RPM does not change the output. Of course the numbers in the RPM rows can be tuned.
In all above considerations, we left the ENGINE TEMPERATURE MAP disabled by entering a constant value. The map values in the RPM/THROTTLE map are multiplied with the values in the A_ENGT map. The engine temperature input can be connected to :
Of course it can be calibrated! Connect the ENGINE TEMPERATURE INPUT to :


All the examples above had a somewhat linear result : at a particular operating point (map point) the output followed the input by the specified map value. With the introduction of the A_ENGT map, the main map values are MULTIPLIED with A_ENGT values, which results in a "THREE DIMENSIONAL" approach, or UNLINEAR output.


The following tuning map demonstrates a THROTTLE/RPM and ENGINE TEMP map.



SMT6 Piggy-Back Unit - Throttle Deflection/RPM and Engine Temperature


At 600 RPM, the output signal is always LESS than the input. However, as the engine temperature increases, the output signal increases at idle. At high engine temperatures, the main map modifications are only HALF (0.5) as effective as at lower temperatures.
The above example may not be that practical. The real practical application depends on what YOUR engine needs. The signal adaptation is relatively easy. If your engine requires temperature adjustment, then the A_ENGT map is good. If your engine requires ABSOLUTE PRESSURE (not manifold) adjustment, then connect a pressure sensor to the engine temperature input and calibrate it accordingly.
The calibration, setting of modes, and all other operations of the SMART TUNER are explained in the relevant manuals and other application notes.