Subaru BRZ Sequential/Dog Engagement Transmission Gear Shift Setup
When Installing a sequential or “Dog Engagement” gearbox and wanting to use a Flat-shift strategy it will be necessary to reduce engine torque during the upshift, this allows the gear “dogs” to release allowing smooth engagement from one gear to the next, this can be achieved using a 0-5V analogue strain gauge input combined with several ProECU custom maps or by simply utilising a superb unit such as the Geartronics Easyshift using a single custom map, if a gear position potentiometer is also fitted to the gearbox the Geartronics Easyshift unit can provide a “closed loop” function meaning full engine torque will only be restored once the next gear is fully engaged, this can protect the dogs on the gears from expensive and premature wear.
Geartronics Unit
http://www.geartronics.co.uk/flatshift.htm
Begin by wiring the Geartronics units Gear Cut Request Signal (Pin 5) into the vehicles ECU “CPC solenoid” input. This enables the ECU to detect the forthcoming gear shift.
The CPC Pressure sensor Input pin to the Subaru BRZ ECU is shown in the image below, pin 5 from the Geartronics Easyshift unit will connect to this input pin.
With the Geartronics Easyshift unit fully wired and set up you can then configure the required Custom Map.
Custom Map Parameter | Setting | Function |
|---|---|---|
Activation | Always Active |
|
Enable | In all drive modes |
|
Output | Ignition Base Timing | Add Map Output To Channel |
X Input | CPC Pressure Sensor V | Select Nearest Cell |
Y Input | Engine RPM | Interpolate Between Cells |
Setting up in this manner allows you to have a reduction of timing (in this example -30 degrees) whenever the Geartronics unit generates the signal from pulling the shift lever, in the example Custom Map above when the voltage sent from the Geartronics unit changes from 5V to 0V (during the shift) and Engine Speed is above 3000 RPM the ignition is retarded.
The Geartronics Easyshift set up software allows you to set up how long the Cut/Retard output lasts, if you use the gear position potentiometer the Cut/Retard time is automatic once the next gear is known to be fully engaged.
Fuel Cut
An additional Custom Map could be set up if Ignition Retard alone does not reduce torque sufficiently to release the gear dogs, the output of this map could be Total Fuel Quantity set to a value of Zero when the map is active.
Downshift Auto Blip/Clutch-less Downshifts
Although this function would be technically possible by utilising the RaceROM AutoBlip function and using the Geartronics unit output connected to the vehicles Clutch Switch input it is not recommended by EcuTek or Geartronics, the throttle blip duration and intensity should ideally vary depending on Engine RPM, Gear, Deceleration Rate and if the vehicle is braking or not, Geartronics have put together a great explanation on the subject in the link below.
http://www.geartronics.co.uk/blippers.htm
Setting up without using the Geartronics Easyshift System.
Although the system cannot provide closed loop control like the Geartronics Easyshift can EcuTek ProECU RaceROM V12.2 and later patches allow you to use a 0-5V output analogue load cell to trigger the shift retard, various re-purposed ECU input pins can be selected as the voltage input.
ProECU then allows you to configure the voltage threshold at which the trigger will be active, other functions such as hysteresis and also the ability to invert the input signal are also configurable, a custom map set up similar to the one shown earlier in this document could then be used for the shift retard function.