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Engine Constants

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From the Settings menu, select Constants

Here you need to setup the engine constants. Fill out the fields in the bottom section before calculating the Required Fuel.


  • Control Algorithm: The load source that will be used for the fuel table
  • Squirts per Engine Cycle: How many squirts will be performed over the duration of the engine cycle (Eg 720 degrees for a 4 stroke). most engines will not require values greater than 4. For sequential installations, this should be set to 2 with the injector staging set to 'Alternating'(Internally Speeduino will adjust the squirts to 1)
    • Note that for 3 and 5 squirts, you must have a cam signal in addition to the crank.
  • Injector Staging: This configures the timing strategy used for the injectors
    • Alternating (Recommended for most installs) - Injectors are timed around each cylinders TDC. The exact closing angle can be specific in the Injector Characteristics dialog.
    • Simultaneous - All injectors are fired together, based on the TDC of cylinder 1.
  • Engine stroke: Whether the engine is 2 stroke or 4 stroke
  • Number of cylinders: Number of cylinders in the engine. For rotary engines, select 4.
  • Injector Port Type: Option isn't used by firmware. Selection currently does not matter
  • Number of injectors: Usually the same as number of cylinders (For port injection)
  • Engine Type: Whether the crank angle between firings is the same for all cylinders. If using an Odd fire engine (Eg Some V-Twins and Buick V6s), the angle for each output channel must be specific.
  • Injector Layout: Specifies how the injectors are wired in
    • Paired: 2 injectors are wires to each channel. The number of channels used is therefore equal to half the number of cylinders.
    • Semi-Sequential: Semi-sequential: Same as paired except that injector channels are mirrored (1&4, 2&3) meaning the number of outputs used are equal to the number of cylinders. Only valid for 4 cylinders or less.
    • Sequential: 1 injector per output and outputs used equals the number of cylinders. Injection is timed over full cycle. Only available for engines with 4 or fewer cylinders.
  • Board Layout: Specifies the input/output pin layout based on which Speeduino board you're using. For specific details of these pin mappings, see the utils.ino file
  • MAP Sample Method: How the MAP sensor readings will be processed:
    • Instantaneous: Every reading is used as it is taken. Makes for a highly fluctuating signal, but can be useful for testing
    • Cycle Average: The average sensor reading across 720 crank degrees is used. This is the recommended option for 4 of more cylinders
    • Cycle Minimum: The lowest value detected across 720 degrees is used. This is the recommended method for less than 4 cylinders or ITBs