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SMT8_4 Technical Manual - Boost Control

SMT8_4 TECHNICAL MANUAL

Perfect Power Online Manuals.

 

Support for your SMT8 V4 Unit.

BOOST CONTROL

The SMT8_4 has a boost control feature, which can be used to IMPLEMENT a boost control loop after adding a turbo.


This does NOT MODIFY and existing boost control loop, but constructs a new one. The manifold pressure is measured via the AMP (IN) (pin 3 of 12) and compared to a target map. Depending on the difference to the target boost pressure the output PWM to the bleeder solenoid is modified so that the waste gate is closed/opened to achieve the target pressure.

 

 

PURPOSE

 

It is often desirable to add a turbo to an engine without DE-COMPRESSING the engine. In this application precise boost control is required at lower RPM to avoid knocking, but higher boost pressures can be used at high RPM.

 

The boost control is achieved via a “BLEEDER” valve, which controls the effective canister pressure, and thus operates the waste gate. The signal to the bleeder valve is PWM.

 

 

BOOST CONTROL MAPS AND PARAMETERS

SMT8V4 Piggy-Back Unit - F8 - Boost Control

 

BOOST TARGET MAP
Entry is in pressure (bar/lbs). For each RPM point a different boost target can be specified.


BOOST AIR TEMPERATURE
The entry is in percent (of PWM). The value is added/subtracted from the PWM base.


BOOST LOW PWM
This is the PWM BASE duty cycle in percent for LOW TPS settings.


BOOST HIGH PWM
This is the PWM BASE duty cycle in percent for HIGH TPS settings.


BOOST GAIN (PARAMETER)
This is a multiplier (0.01 to 9.99) by which the target to manifold difference is multiplied with before adding the result to the BASE PWM. If the actual manifold pressure differs too much from the target then the gain is too low. If the loop ‘oscillates’ then the gain is too high. The gain depends on the bleeder valve construction, the size of the waste gate canister, and the piping used.

SMT8V4 Piggy-Back Unit - ShiftF1 - Parameters

SMT8V4 Piggy-Back Unit - Diagram of Typical Boost Solenoid

DIAGRAM OF TYPICAL BOOST SOLENOID

 

 

WASTE GATE CANISTER

 

A waste gate canister with a pressure of less or equal to the LOWEST boost pressure must be used. Normally 0.2-0.3 bar (3.5lb) is sufficient.