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Smart Tuner SMT8-L - Boost Control | Application Note : AN 5


Perfect Power Application Notes.


Application Note - AN 5


The SMT8-L has electronic boost control. This application will show how to wire and configure the boost.


Boost Control is handy when you want more boost than what the regulating canister is set to. Different boost pressures can be set for rising RPM so at low RPM where the engine is likely to detonate the boost can be low and at high RPM the boost can be increased when detonation is less likely to occur.


SMT8L Boost Wiring


 SMT8-L Piggy-Back Unit - Boost Wiring



SMT8-L Boost Setup

There are 4 main boost maps. Low throttle position PWM vs RPM. High throttle position PWM vs RPM. PWM vs Air Temp. Boost target AMP vs RPM. Boost gain parameter and boost output system definition.
SMT8-L Piggy-Back Unit - Boost Setup
SMT8-L Piggy-Back Unit - F7 - Boost Control
SMT8-L Piggy-Back Unit - ShiftF2 - System Definition

SMT8L Boost setup open loop

Enable the Boost output in the Shift F2 System Definition map. Set the Boost gain to 0.00 in the Shift F1 Parameters map. First time tuning the boost it is recommended to use the Low and high throttle PWM maps to get close to the actual boost pressure you want for the complete rev range. The low and high PWM maps are for throttle positions less than half throttle for the Low PWM and higher than half throttle for High PWM. These two maps are percentage based so values from 0-99 are accepted. Input values until you have the required boost pressure. The Air Temp PWM can also be set to increase or decrease the boost at different air temperatures. The Air Temp PWM map can accept negative entries. At this point you have "open loop" boost control. Open loop means that the SMT8 will not adjust the boost PWM if the target boost pressure varies from your original setting.

SMT8L Boost Setup Closed Loop

Closed loop boost control is done after the open loop boost control is setup. Please see above on how to setup open loop boost. Open the parameters map and set the boost gain to a value higher than zero. Zero in the boost gain disables the closed loop. In the boost AMP target map set the boost pressure you want for each RPM. If the boost overshoots your target then the boost gain is too large. If the boost pressure doesn't reach your target then the boost gain is too small. The SMT8L will now regulate the PWM output to reach your target boost pressure.
Note : The target boost pressure map is above atmospheric pressure. Example : if your atmospheric pressure is 0.86 bar and you want to have 0.5 bar boost the target would be 0.86 + 0.5 = 1.36.
Note : Closed loop is only possible if a map sensor which can read the boost up to or more than your boost target is wired into the SMT8L.
SMT8-L Piggy-Back Unit - ShiftF1 - Parameters
SMT8-L Piggy-Back Unit - Boost AMP Target
Note : The SMT8L boost control cannot reduce the boost to lower than the canister rating. To check the exact boost PWM use the data display and display the boost PWM as a large or small number.


Closed or open loop boost control is made easy with the SMT8-L boost circuit.