Introduction

Installing a Greddy boost controller on your Dodge Stealth is one of the most effective ways to unlock extra horsepower from the twin-turbo 3.0L V6. By allowing precise control over wastegate actuation, you can safely raise boost from the factory 12-13 PSI up to 20 PSI. This guide covers the entire installation process, from component selection to final tuning, so you can enjoy a noticeable power increase without compromising reliability.

Understanding Boost Controllers and Your Dodge Stealth

Why a Boost Controller?

The factory electronic boost control system on the Stealth (and its sibling the 3000GT) is conservative. It uses a combination of wastegate actuators and an electronic solenoid that can limit boost due to knock detection. A manual boost controller like the Greddy Profec unit bypasses this complexity, letting you set a consistent boost level. This is especially valuable when running higher boost than stock, as the factory solenoid may not hold steady pressure under load.

The Greddy Boost Controller: Key Features

Greddy offers several boost controller models, but the most common for the Stealth community is the Profec B Spec 2 or the simpler Profec (manual) unit. These controllers feature an adjustable knob or digital interface for setting boost, and they operate by bleeding off pressure from the wastegate actuator line. The Greddy unit is known for its reliability and ease of adjustment, making it a popular choice for intermediate tuners.

Safety Considerations Before You Begin

Running 20 PSI on a stock Dodge Stealth requires careful preparation. The stock fuel system, injectors, and intercooler are typically capable of supporting up to about 15-16 PSI safely. Beyond that, you risk fuel starvation, detonation, and engine damage. Before proceeding, ensure your vehicle has adequate fuel delivery, proper ignition timing, and either a standalone or piggyback engine management system or at least a fuel cut defender. This guide assumes you have upgraded your fuel system and have a boost gauge installed. If not, stop here and address those items first.

Tools and Materials Needed

  • Greddy boost controller kit (Profec manual or electronic)
  • Socket set (metric, 8-14 mm)
  • Screwdriver set (flathead and Phillips)
  • Wire strippers and crimpers
  • Electrical tape and heat shrink tubing
  • Vacuum hose (silicone or rubber, 4 mm or 1/8” ID)
  • Boost gauge (already installed, essential for monitoring)
  • Multimeter (for checking continuity and voltage)
  • Zipties for cable management
  • Shop manual or wiring diagram for your Stealth year (1991-1996)

Step 1: Preparation and Safety

Parking and Battery Disconnection

Park your Stealth on a level surface and let the engine cool completely. Disconnect the negative battery terminal to prevent any short circuits during wiring. Wait at least 10 minutes after engine shutdown before working in the engine bay to allow the turbochargers to cool.

Engine Bay Assessment

Open the hood and locate the turbochargers. On the Stealth, the two turbos sit at the front of the engine (facing the radiator). The wastegate actuators are attached to each turbo. Identify the vacuum lines controlling these actuators: a small rubber hose runs from each wastegate to a T-connection that then goes to the factory solenoid or directly to intake manifold pressure. Note that the Greddy controller will intercept this line. Also locate the intake manifold vacuum source for the controller’s pressure reference port.

Step 2: Installing the Boost Controller Unit

Mounting Location Guidelines

The Greddy controller should be mounted within easy reach of the driver for quick adjustments. Common locations include the passenger side footwell, under the dashboard, or inside the center console. Avoid mounting it near heat sources or moving parts. If you choose the engine bay, use the provided bracket on a flat surface away from the exhaust manifold. For electronic controllers, drill small holes for mounting screws and secure the bracket firmly.

Securing the Controller

Once the location is chosen, use the supplied screws and bracket to attach the controller. For a clean installation, route the wiring and vacuum lines before tightening everything permanently. Ensure the controller is mounted upright to prevent any internal pressure sensor errors.

Step 3: Connecting Vacuum Lines

Identifying Vacuum Sources

The Greddy controller has three ports: INPUT (from turbo pressure source), OUTPUT (to wastegate actuators), and a small vent (bleed) port. The INPUT port must be connected to a pressure source that sees actual boost—usually a vacuum line from the intake manifold or directly from a compressor outlet. The OUTPUT port goes to both wastegate actuators. On the Stealth twin-turbo, you will T the output line to both wastegates. The vent port should be left open or with a short piece of hose pointed downward to prevent debris ingress.

Proper Hose Routing and Sealing

Cut fresh vacuum hose to the required lengths. Use nylon zip ties or clamps at each connection to prevent boost leaks. A leak at the wastegate line can cause overboost, while a leak at the input line will cause low boost. Check all connections with the engine running (after assembly) using soapy water to detect bubbles. Double-check that no hose is kinked or melted against hot surfaces.

Step 4: Electrical Wiring

Power and Ground Connections

For electronic controllers, wire the red wire to a switched 12V source (use a fuse tap from the interior fuse box for clean power) and the black wire to a solid chassis ground. Avoid grounding to the battery negative terminal to reduce electrical noise. For manual controllers, there is no wiring—only vacuum lines. The original text’s “wiring the boost controller” typically applies to electronic units; clarify which model you have.

Wiring the Solenoid (if applicable)

If your Greddy controller includes an external solenoid (as in the Profec A/B series), mount the solenoid away from heat and vibration. Connect the solenoid’s wires to the controller unit per the supplied diagram. Use a multimeter to verify continuity on the solenoid coil before final connection. Wrap all exposed terminals with heat shrink tubing and electrical tape.

Step 5: Final Assembly and Reconnection

After routing and connecting all vacuum lines and wiring, reinstall any panels removed for access. Check that no tools or loose parts remain in the engine bay. Reconnect the battery terminal, ensuring a clean, tight connection. Start the engine and let it idle for a few minutes while inspecting for vacuum leaks. The idle should remain smooth; if it hunts, there may be a vacuum leak at the controller’s reference port.

Step 6: Setting Boost Level to 20 PSI

Initial Startup and Warm-Up

With the engine warm and the controller set to its lowest boost setting (fully turned counterclockwise), do a brief test drive at light throttle to verify that the car makes stock boost (approximately 10-12 PSI on the gauge). Gradually increase the controller setting in small increments while monitoring the boost gauge during a full-throttle pull in 3rd gear. Do not exceed 15 PSI on the first attempt—verify that boost is stable and not spiking.

Adjusting the Controller

Turn the adjustment knob or digital dial clockwise to increase boost. A quarter-turn typically raises boost by 2-3 PSI. Make small adjustments and then drive the car to see the effect. When you reach 20 PSI, pay close attention to engine sounds—any detonation (metallic knocking) means you must immediately reduce boost. If the car runs smoothly at 20 PSI, you can lock the adjustment ring (if present) to prevent accidental changes.

Monitoring with a Boost Gauge

A reliable boost gauge is non-negotiable. The factory gauge is not accurate enough for precise tuning. Install an aftermarket mechanical or electronic gauge plumbed into a dedicated vacuum line from the intake manifold. Watch for peak boost, boost spikes (transient overboost), and boost creep (boost that continues to rise beyond the set point at high RPM). Spikes above 22 PSI require immediate investigation.

Step 7: Testing and Fine-Tuning

Test Drive Protocol

Perform a series of pulls from 2000 RPM to redline in 3rd gear on a safe, empty road. Log the boost readings and note any hesitation or surging. Also test in 4th gear under load (like on a slight uphill) to simulate real-world conditions. The controller should maintain steady boost within 1 PSI of the set point.

Checking for Boost Creep or Spikes

If boost rises above 20 PSI after the set point, you may have a leaky wastegate actuator or improper line routing. Check that the wastegate actuators open fully. You can also adjust the controller’s “gain” or “response” setting (on electronic units) to reduce spikes. If using a manual controller, a small adjustment screw inside the unit can fine-tune the rate of pressure bleed.

Making Adjustments

After several test runs, you may need to revisit the controller adjustment to eliminate mild boost creep. Also consider the time of year—colder air denser air can increase effective boost. Recheck the setting during cooler weather. Keep a log of adjustments for future reference.

Troubleshooting Common Issues

  • Boost lower than set: Check for vacuum leaks at the controller’s input port or wastegate lines. Also verify wastegate actuator diaphragm integrity—apply vacuum to test if they open.
  • Boost spikes or overboost: The wastegate lines may be too long, causing lag. Shorten hoses. Also ensure the controller’s bleed port is not blocked. On electronic units, reduce gain.
  • Boost oscillation (surging): This occurs when the controller and wastegate fight each other. Increase the controller’s gain (if adjustable) or use a restrictor in the vacuum line.
  • Engine detonation at 20 PSI: Reduce boost immediately. Check fuel pressure, injector duty cycle, and ignition timing. Consider adding water/methanol injection or upgrading to a standalone ECU.
  • Controller not holding setting: Dirt or debris inside the adjustment mechanism. Clean with contact cleaner and re-calibrate.
  • Electrical controller not powering up: Blown fuse or poor ground. Test with multimeter at the unit’s power connector.

Supporting Modifications for 20 PSI Boost

Fuel System Upgrades

Stock injectors (360cc/min) will exceed 80% duty cycle before 16 PSI. For 20 PSI, upgrade to 550cc or 650cc injectors. You will need a fuel pressure regulator and a rising-rate pressure regulator or a tune from a chip or standalone ECU. Do not run 20 PSI without proper fueling—lean conditions will destroy pistons quickly.

Ignition Timing and Intercooling

Retarding ignition timing by 2-4 degrees across the RPM range helps prevent knock at high boost. A good intercooler upgrade (front-mount or larger side-mount) reduces intake air temperatures. Also consider upgrading the bypass valve to a blow-off valve that holds boost pressure better.

Engine Management Tuning

While a boost controller can raise boost, the factory ECU will pull fuel and timing if it sees knock or high intake airflow. A piggyback (like Apexi SAFC) or a full standalone (Haltech, AEM) is recommended to adjust fuel and timing maps for 20 PSI. For a simpler route, a pre-tuned chip from a reputable 3S tuner (e.g., 3SX Performance) can provide a safe base tune.

Conclusion

Installing a Greddy boost controller on your Dodge Stealth is a straightforward process that yields excellent results when done correctly. By following this expanded guide, you can safely run 20 PSI and enjoy a substantial power increase over stock. Remember that boost control is only one part of the equation—proper fuel delivery, ignition control, and heat management are essential for reliability. Test thoroughly, log your data, and don’t hesitate to consult the 3S community forums for model-specific advice. With careful tuning, your Stealth will deliver the performance you’ve always wanted.