How to Set-Up Transmission Dump Valves

Transmission dump valves have become essential components in competitive heads-up race cars. In this guide, we will walk you through how to configure them in your FTManager software, allowing you to make the most of your FuelTech engine management system.

A transmission dump valve is a fluid bypass device that temporarily reduces torque converter pressure, allowing the engine to run with less resistance. This aids in turbo spooling, reaching higher RPMs on the 2-step, and managing power based on the racing surface.

There are two primary types of dump valves used in modern racing transmissions: internal and external. While implementations may vary among transmission builders (e.g., Powerglide vs. TH400), we will cover the general concepts.

External dump valves typically bypass fluid from the cooler circuit directly to the transmission pan, allowing more fluid than usual to escape the converter and lowering the drive pressure. It's common to have multiple external dump valves on a single transmission. This setup mildly loosens the converter and can be used throughout the track, making it a valuable tuning tool.

An internal dump valve redirects the fluid feed from the converter back to the pan, significantly reducing converter drive pressure by "starving" the converter of fluid. However, this can damage the converter if used for too long under load. It's recommended to use this only for turbo spooling and to shut it off before the car leaves the starting line. This method drastically loosens the converter and is used only on the transbrake, not down the track.

We will discuss the most common strategies for using these valves and explain why and how they work.

By following these guidelines, you can optimize the performance of your transmission dump valves and gain a competitive edge on the race track.

Controlling an external dump valve is generally straightforward, with no concerns if used during the pass.

Control Strategies Include:

This is the simplest on/off control strategy. It includes a checkbox to activate the valve on the transbrake and a timer to set when the valve turns on and off during the pass. For example, you can configure it to activate on the transbrake and turn off 1 second into the run.

This method offers more parameters to configure, such as minimum TPS and various control options like MAP, RPM, and more. It can also be PWM operated if desired.

Example Setup: Similar to the previous method, you can set it to activate with the transbrake and remain active for 1 second into the pass. Additionally, you can fine-tune the control using parameters like:

• Minimum TPS: Sets the minimum throttle position to activate the valve.

• Control Options: Utilize MAP, RPM, or other metrics for more precise control.

• PWM Operation: Allows for pulse-width modulation if needed.

This approach provides greater flexibility and precision in managing the external dump valve during the race.

In the control table below, you’ll notice an extra breakpoint at 1.01 seconds. This breakpoint ensures a definite stopping point for the valve operation. Without this, the PWM percentage would continue to ramp down to 0% over 2 seconds.

By adding the breakpoint at 1.01 seconds, you ensure precise control and prevent unintended gradual reduction of the PWM signal, maintaining the desired performance throughout the pass.  

One of the most effective methods for using an internal dump valve is through boost-activated outputs. This method can also be applied to external dump valves.

Example Setup: If you aim to make 8+ psi of boost on the transbrake and leave the line with the valve closed, you can configure the system as follows:

• Activation Conditions: The internal dump valve is set to activate only when the transbrake is engaged. Additionally, it requires at least 0.5 psi of boost, RPM greater than 2200, and throttle position more than 40% to turn on. This prevents accidental activation, such as when holding the transbrake to reverse the car.

• Deactivation Conditions: The internal dump valve will remain active until the ECU detects 7 psi of boost, at which point it will turn off. At this boost level and RPM, the engine typically generates enough power to maintain high RPM on the converter and continue spooling effectively.

While there are various advanced features available for controlling dump valves, the methods discussed here are the simpler and more commonly used ones. If you decide to use dump valves, we strongly recommend installing a converter pressure sensor, such as the PS-500 Pressure Sensor (0-500 psi sensor).

Benefits of a Converter Pressure Sensor:

• Logging and Monitoring: It allows you to log and monitor converter pressure, providing valuable data on how the converter is performing under different conditions.

• Transmission Tuning: The data can be highly beneficial for your transmission builder, enabling them to make precise adjustments to optimize performance.

By integrating a converter pressure sensor, you can enhance the effectiveness of your dump valve setup and ensure your transmission operates at peak efficiency.

As always, FuelTech's industry leading tech support is available to answer your questions!