If you are new in setting up an open loop boost control, extra care should be taken to avoid exceeding the limits of the engine. These steps will help and guide you in the starting stage.
What you need:
3 Port Mac Valve
We highly recommend you to use a 3 port MAC valve to control boost. These are widely available and we also keep them in stock.
If you are using an external waste gate actuator with a single port, the compressor exit before the throttle body connected to port 3, and port 2 should be connected to the waste gate actuator. This means that when the valve is off, the actuator sees the boost pressure and it is set by the spring in the actuator. When the valve is on, the actuator sees atmospheric pressure and the spring holds the waste gate shut.
If you are using a dual port actuator, the compressor exit should be connected to both the underside of the diaphragm and port 1 on the valve. Port 2 on the valve connects to the top side of the diaphragm. This means that when the valve is off, the top side of the diaphragm sees atmospheric pressure while the bottom side sees boost pressure, resulting in the boost set by the actuator spring. When the valve is on, both sides of the diaphragm see boost pressure and the spring holds the waste gate shut.
Auxiliary Output
You will need to connect one side of the MAC valve to an aux output on the ECU. If it’s a 420c or a Select, you need to use auxiliary output 1, 2 or 3, because those are pulse width modulation capable. The other side of the MAC valve needs to be connected to ignition switched +12V. You then need to configure that output as a waste gate control and enable PWM and select 25 Hz as the PWM frequency.
Waste Gate Screen
On the waste gate screen, you need to select the maximum duty cycle as 100% and the minimum throttle and MAP. The ECU will need to see before it activates the valve. Below this, the output on the ECU will be switched off. This saves wear on the valve as well as noise when you only need the waste gate boost pressure. On the waste gate screen, you can select the duty cycle on the valve that you need at each RPM to get the boost curve that you want.
In practice, this is normally done by trial and error. But a good place to start is this formula:
How to Run Boost by Gear
Many cars, especially high poweed circuit cars, and turbocharged front wheel drives, can benefit from having different boost settings in different gears. These steps show you how to set this up:
Step 1: Add speed sensor (s)
If you already have a good Hall effect sensor on the gearbox output, you can just connect this into the ECU master vehicle speed sensor input (MVSS1). If the car doesn’t have a good sensor on the gearbox, you can add them to the two driven wheels (front wheels on a front wheel drive car) anc connect them into MVSS1 and MVSS2 inputs. If you are going to do that, you need to use a Select Plug-in ECU or a 440 (not an e420d basic, as the e420d Basic only has a single vehicle speed input). On many cars it is possible to trigger the sensor using the back of the wheel studs. This page shows the front wheel speed sensors on the Adaptronic Mazda MX5.
If you’re using Hall effect (digital) sensors, you must select “Digital” under “MVSS Mode”, and also enable either MVSS1 or both MVSS1 and MVSS2, depending on the ones that are being used:
Step 2: Mounting the sensor and wiring it up
If you are adding sensors to the vehicle, The best sensors we find are the Honeywell GT101 sensor and we keep these in stock. If the car has holes in the brake backing plate that line up with the wheel studs then the sensor can be triggered by the wheel studs as the wheel rotates. Being Hall Effect, they work in the steady-state which means that when the sensor is facing the back of the stud, the output is low. And when the sensor is not facing the back of the stud, the output is high. The sensors need a supply which can usually be either 5V or 12V, a signal ground which connects back to the ECU sensor GND, and a digital output which connects to the appropriate VSS input on the ECU.
Step 3: Test the hardwave
After mounting the sensor and wiring it up, you should check if it works by rotating the wheel by hand and that the MVSS input triggers correctly when you look at the diagnostic window which by hitting F11. In the F11 window, check that MVSS (and/or MVSS2) show green when the sensor is not being triggered, and red when it is being triggered. It will flash yellow as the trigger is changing, so a wheel spinning continuously should show the MVSS / MVSS2 indicator in yellow.
Step 4: Calibrate the speed sensors
Once you’ve confirmed that the sensors are working, you must calibrate them by driving at 50 km/h and clicking the “Learn” button. This is best done with a passenger assistant or on a dyno for obvious reasons. The figure below shows this calibrated for two wheel speed sensors (both wheel speed sensors on the Adaptronic turbo Mazda 121):
By following these steps, you will have a correct MVSS reading on your gauge window.
Step 5: Calibrate the gear ratios
To calibrate the gear ratios, you must then drive in each gear and click the “Learn” button for each gear so that the ECU can learn the ratio between road speed and engine speed. You will also need to set the value of “tolerance” on how close these need to be (a value of 120, which corresponds a 12% difference between the measured speed and the theoretical speed, is typical). You can check in the F11 window if the ECU is detecting the current gear correctly:
Step 6: Set the boost duty cycle in each gear
All you need to do to engage boost by gear in open loop boost mode is to put in the waste gate duty cycle that you want the ECU to limit to when you are in each gear (on the road speed page).
Through all these steps, you can now have a boost by gear with just a MAC valve and a speed sensor.
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