We are often asked when handling both DCT and 8HP transmission swaps how to make the engine throttle cut and blip. First off, blips and cuts make the most of these extremely quick shifting modern transmissions. It is important to use an electronic throttle body when going for seamless gear changes. One can have a much faster shift and keep it smooth when the throttle can cut and blip during shifts compared to not. However, many of our customers are using factory ECU's that don't understand such commands or standalone ECU's that aren't very "smart" when it comes to adjusting how much and how long to cut and blip for.
The great thing about the HTG GCU is that it can handle all cuts and blips internally, and also offers extremely easy to tune settings for them. In the future the GCU will offer closed loop control of blips and cuts as well, making the most out of every shift. The HTG GCU function that control blips and cuts is called the DBWMOD; the Drive By Wire Modifier. What it does is intercept the accelerator pedal signals, mirror them, and then modify them (+-) slightly if a cut or blip is commanded. The modified pedal signal is then sent back to the ECU. This can be integrated two ways.
The Hotwire Method:
The hotwire is the best way to integrate the DBWMOD function into an existing wiring harness, such as a car with an factory ECU and harness, or a race car that already has been wired. All you are going to do is cut the two signal wires coming out of the accelerator pedal connector, we have many examples of these pinouts below, and instead wire the HTG between the pedal and where the wires were originally going (ECU).
The diagram below is showing the hotwire method. The vehicle's pedal 5v supply and sensor ground are untouched. The two wires going from the pedal to ECU now first go to the GCU into any available analog input. From there the signal is modified and sent via and of the GCU's analog outputs back to the wires that were cut that go to analog inputs in the ECU.
If you are wiring a car from scratch it is preferable to wire the pedal fully to the GCU as seen below. This can help minimize any interference that may occur. The only wires going to the ECU with this method are the modified accelerator pedal position signals from the HTG via any available analog output. 5v supply and sensor ground are supplied by the GCU.
Always try to wake up the GCU before the ECU wakes up. This can help avoid any fail-safes in the ECU that don't see a pedal signal for the split second the GCU needs to wake up. This is not always necessary depending on ECU but is best practice. To wake up the GCU send 12v power to its L1 pin. A common simple way to do this is to wake up the GCU using key position1 and waking up the ECU when you get to key position 2. You can also use a switch to turn on the ecu after the ecu wakes up.
Setting up the DBWMOD is also very easy to do in the software. First, enable the DBWMOD on the general settings page. The bottom right box will have the only thing you need to change. In the "Enable DBW Mod" Select 'ENABLED' as shown below. You do not need to change anything else on here.
Next you want to configure the APP signals coming and going from the HTG from the pedal. This often done using the first two analog inputs and outputs available as shown below. If you are using the hotwire method, select 5v in the range column. If you are fully wired select GCU 5v (it runs slightly higher 5.15v). For the GCU to mirror the pedal signal completely, leave all Min/Max settings 0. Note it always important to use a brake signal for the GCU to work best.
If your ECU is not compatible with the range the pedal has, or you want to add a dead spot you can also adjust the inputs and outputs as an example shows below. A helpful tool for doing this can be found here: https://www.seemslegitgarage.com/post/htg-analog-input-setup
The final step is to set up the map settings. These are found under the "DBW mod" tab. You will want to drive the car a little and see the how much calculated torque the engine makes first. Once you understand this scale you can easily understand how much more or less blip or cut you may need on the map graphs. Another helpful hint is after a shift is completed the cell that was used for the GCU calculation will have a black box appear around it. For that shift you can adjust that box and its surrounding area until it feels perfect. Settings below are a good starting point. The best way to tune this is to ride as passenger and have someone else drive and perform shifts you call out.
Thank you for reading! If you have any questions please feel free to reach out to us for support.