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SMT8_4 Technical Manual - Altitude Compensation


Perfect Power Online Manuals.


Support for your SMT8 V4 Unit.


The general principle is simple: at an elevated altitude the air is thinner, therefore the engine needs less fuel. Without compensation the engine runs rich, which is sometimes a desirable effect.

However, in a piggyback environment, things can get a little tricky. Most likely the engine was modified, and the stock ECU compensation algorithm is not known. If things get out of shape then the SMT8 can help and rectify the situation.

The altitude compensation requires extra hardware. The output of a standard 1.15Bar pressure sensor MPX4115 must be connected to the special analogue input as a means of measuring the ambient pressure.

NOTE: The pressure sensor requires 5V supply. A dds part for 12V connection is available.


Connections : ASPCIN Pin 7-12
Enabling :
System definition: Altitude Comp.Enable
Direction :
System definition: Altitude Comp.Increase
Map :
Acceleration Altitude Comp Map: FACTOR


Compensation calculations:

The unit computes a ratio from the measures ambient pressure (ASPCIN) to 1.00 BAR. This ratio is multiplied with the map entry to form the final compensation ratio. If enabled, the fuel is modified by this ratio.

The fuel can be increased or decreased at an altitude.



  • The calibration of the MPX4115 is built in.
  • Pressures below 0.7bar (approx. 3000 Meter) are not recognized.