These boost control parameters determine how the ECU controls the boost control solenoid.
Enabling Boost Control
Pin A11(US, unused EGR output) or pin A17(JDM, IAB control output) is used to run the boost control solenoid, as it is a duty cycle controlled output. For JDM ECU's, the variable frequency option must be selected in order for boost control to function properly.
Solenoid Configuration
There are two types of solenoid - normally open and normally closed. A normally open solenoid (like the GM solenoid) will give maximum boost at 0% duty. Note that in this case SManager inverts the duty cycle so that in SManager 0% duty cycle is minimum boost, and 100% duty cycle is maximum boost. It is important to set a boost limit as a solenoid or wiring failure will result in maximum boost.
Duty Cycle
To control the solenoid a square wave is sent to the solenoid. Due to the impedance of the solenoid and frequency of the output this square wave results in a progressive opening (or closing) of the solenoid The solenoid will have an effective range, outside which changing the duty cycle will not affect the solenoid opening. For the GM solenoid this is 15% to 85% duty cycle, so it not recommended to operate the solenoid outside these limits.
Variable Frequency
The frequency of the solenoid control output waveform can be set from 10 - 80 Hz
Most solenoids operate best from 30-60 Hz.
Control Method
There are three methods for determining the boost control solenoid duty cycle. When the settings are configured for a normally open solenoid the actual duty cycle is inverted so that a higher duty cycle will increase boost.
Fixed duty cycle
This setting will output a fixed duty cycle to the solenoid once the solenoid activation pressure is reached, and should give a fairly flat boost curve which is the same in each gear. It is useful for setting up the pressure vs duty cycle table, or testing the boost control output.
Gear based duty cycle
This setting will output a duty cycle based on the boost by rpm & gear table. The pressure vs duty cycle table is not used with this setting.
Gear based target boost
With this setting the boost by rpm & gear table is first used to lookup the target boost level, then the pressure vs duty cycle table is used to calculate the solenoid duty cycle to reach the target boost.
Solenoid activation pressure sets the point where ECU starts to use the solenoid to control boost pressure. Normally this can be set a little below the minimum boost pressure in order to minimize wear on the solenoid.
Pressure vs Duty Cycle
The Pressure vs Duty Cycle table contains a lookup of pressure valves which correspond to a solenoid duty cycle. The values for this table must be set by using a fixed duty cycle (see Control Method) and noting the resulting manifold pressure. Note that different ambient conditions will result in slightly different boost pressures for the same duty cycle.
This allows two different boost settings (by gear) to be used, based on a switch input. Typically these two boost settings would be used for wet/dry conditions, high/low octane fuel or normal/drag tires.
Note that if an ethanol / Flex Fuel input is being used then the Ethanol Boost Compensation can interpolate between the low and high target boost table values.
Boost by Rpm & Gear
These tables set the target boost for each gear and rpm. The pressure units are determined by the unit used for the solenoid activation pressure. Note that these tables can also be used to set boost by speed and gear.
Air Temperature Compensation
The boost pressure for a given duty cycle will vary with ambient air temperature, with increased pressure with cooler air and less pressure with hotter air. This table allows you to adjust the duty cycle based on intake air temperature. The compensation is only applied when using boost by gear - the air temperature compensation is not applied to the fixed duty cycle value.
Throttle Position Compensation
The duty cycle can be reduced with decreasing throttle so that the throttle pedal can be used to control the boost level.
Quick Spool
This tables opens up the boost control solenoid completely and closes the waste gate to build up boost faster. Once the pressure reaches the value in the table the solenoid goes back to its normal duty cycle. When using this feature, we recommend setting the solenoid activation pressure to 1 pound of boost, and the quick spool pressures to 1 or 2 pounds below target boost levels. To disable quick spool, set the values in the table lower than the solenoid activation pressure
Maximum Boost By Speed
This tables limits the boost control duty by vehicle speed and pressure or duty cycle. Note that a rear wheel speed sensor is required to get best use of this table.