Understanding the Aeromotive Stealth Fuel Pressure Regulator

The Aeromotive Stealth Fuel Pressure Regulator is a return-style bypass regulator engineered for high-horsepower LS engine swaps and performance builds. Unlike many external regulators, the Stealth is designed to mount directly on the fuel rail, eliminating the need for a separate mounting bracket and long hose runs. Its compact billet aluminum body houses a precision-machined piston and diaphragm assembly that maintains a steady fuel pressure regardless of pump flow or throttle position. This design is particularly beneficial for LS engines, which rely on consistent fuel delivery across a wide rpm range to avoid lean conditions under boost or high load.

The "Stealth" name refers to its ability to be tucked away neatly in the engine bay. Many LS swaps suffer from clutter around the intake manifold; this regulator mounts inline with the factory-style fuel rail adapters, keeping the installation clean and serviceable. It is compatible with gasoline, E85, and methanol blends, making it a versatile choice for flex-fuel conversions. For builders targeting 600–1,200 wheel horsepower, the Stealth provides the flow capacity needed without requiring a bulky external unit.

Why Upgrade the Fuel Pressure Regulator on a Chevy LS?

Factory LS fuel systems use a returnless design with a pressure regulator built into the fuel pump module. While adequate for stock power levels, this setup cannot maintain consistent pressure when injector flow rates increase or when the engine demands significantly more fuel. Upgrading to a return-style system with a high-quality regulator like the Aeromotive Stealth offers several concrete advantages:

  • Stable pressure under high flow: The Stealth uses a spring-loaded bypass valve that opens as fuel demand decreases, returning excess fuel to the tank. This prevents pressure spikes and maintains a steady set point (typically 58 psi for LS engines, adjustable from 40–70 psi).
  • Improved fuel cooling: Return-style systems cycle fuel through the rail and back to the tank, cooling injectors and preventing vapor lock—especially important on hot engine bays or boosted LS builds.
  • Greater tuning flexibility: With an adjustable regulator, tuners can change base fuel pressure to alter injector duty cycles and fine-tune air-fuel ratios without swapping injectors.
  • Durability: Aeromotive uses stainless steel internals and a reinforced diaphragm that withstands high ethanol content and sustained high pressure, unlike some cheaper units that fail after a few thousand miles.

Installation Guide for Chevy LS Engines

Installing the Aeromotive Stealth regulator on an LS engine is a straightforward job for someone with basic mechanical skills, but attention to detail is critical. Improper mounting or leaky fittings can cause dangerous fuel leaks. Below is a comprehensive step-by-step process covering tools, preparation, and execution.

Tools and Materials Required

Before starting, gather the following items. Many of these you may already own, but some are specific to the LS fuel system.

  • Aeromotive Stealth Fuel Pressure Regulator (part number 13136 for LS-style rails)
  • Fuel rail adapter kit (often included with the regulator, but verify compatibility with your specific LS intake manifold)
  • 6AN or 8AN fuel fittings (depending on your pump and line size; most LS builds use -6 for return and -8 for supply)
  • PTFE-lined stainless braided hose or nylon fuel line (ensure E85 compatibility if using ethanol)
  • Fuel pressure gauge (0–100 psi range, preferably liquid-filled for vibration resistance)
  • Wrenches: 1/2", 9/16", 5/8", 11/16" for AN fittings; metric for factory fuel rail fasteners
  • Teflon tape or thread sealant (use only a small amount on pipe thread, never on O-ring fittings)
  • Safety glasses and nitrile gloves
  • Shop towels and a fire extinguisher rated for fuel fires

Step 1: Safety Preparation

Disconnect the negative battery terminal. Relieve fuel system pressure by removing the fuel pump fuse and cranking the engine for a few seconds, or by pulling the fuel pump relay and letting the engine stall. For LS engines, the Schrader valve on the passenger-side fuel rail can also be depressed with a rag to release residual pressure. Work in a well-ventilated area and keep all ignition sources away.

Step 2: Remove the Factory Fuel Rail and Regulator

On most LS swaps, the factory fuel rail is a one-piece aluminum rail mounted over the injectors. The factory regulator is usually integrated into the pump module or located at the front of the driver-side rail (on truck engines). If you are converting from returnless to return style, you will need to cap the existing supply line and run a new return line from the rail back to the tank.

Use a fuel line disconnect tool to separate the quick-connect fittings. Remove the fasteners holding the fuel rail to the intake manifold (typically 10mm or 8mm bolts). Lift the rail gently to avoid damaging the injector O-rings. Place the injectors in a clean bag if you are removing them entirely.

Step 3: Install the Aeromotive Stealth Regulator

The Stealth regulator is designed to mount directly on the passenger-side fuel rail in place of the factory crossover tube. Install the included mounting studs or adapter plate onto the rail. Use a small amount of thread sealant on the NPT ports (but not on the O-ring ports). Tighten the regulator body to the rail using the supplied Allen bolts; torque to 20–25 in-lbs to avoid warping the sealing surfaces.

For engines with aftermarket intake manifolds (e.g., Holley, Edelbrock, or aftermarket LS intakes), you may need to install the regulator on a remote bracket if the rail lacks a dedicated port. Aeromotive sells a remote mount kit (part 13139) that includes a bracket and braided hoses for these applications. The Stealth can be mounted either vertically or horizontally, but avoid installing it upside down to ensure air does not become trapped in the diaphragm chamber.

Step 4: Connect Fuel Lines

Route the fuel supply line from your pump (typically -8 AN) to the inlet of the fuel rail. Use a high-flow fuel filter between the pump and the rail. Connect the return line from the Aeromotive regulator's outlet to the fuel tank. The return line should be at least -6 AN to prevent back-pressure. Ensure all AN fittings are properly cinched with wrenches—hand-tightening AN fittings often leads to leaks.

If you are retaining the factory fuel pump, note that stock pumps often cannot maintain pressure in a return-style system without a dedicated pump controller or rewire kit. Consider upgrading to a Walbro 450 or Aeromotive 340 pump for reliable flow above 500 hp.

Step 5: Prime System and Check for Leaks

Reconnect the battery. Temporarily bypass the fuel pump relay to power the pump directly, or key-cycle the vehicle (if using factory ECU control) to prime the system. Listen for the pump to prime and watch for any fuel weeping from connections. Use a clean shop towel to check each fitting. If a leak is found, depressurize the system (disconnect power to pump and open the rail pressure bleed) before tightening.

Once no external leaks are present, attach a fuel pressure gauge to the regulator's diagnostic port (some Stealth models include a 1/8" NPT port for a gauge). Adjust the regulator by turning the Allen screw clockwise to increase pressure, counterclockwise to decrease. For naturally aspirated LS engines, set base pressure to 58 psi with the vacuum line disconnected. For boosted applications, initial setting is typically 58 psi plus boost reference (e.g., 1:1 rise rate).

Step 6: Final Checks and Road Testing

Start the engine and let it idle while monitoring the gauge. Confirm pressure holds steady within 1–2 psi of the set point. Drive the vehicle gently, then perform a full-throttle pull on a closed road or dyno to verify there is no pressure drop under load. Check for fuel smell or drips after the engine bay heat cycles. Re-torque fittings after the first 100 miles as thermal expansion can slightly loosen connections.

Cost Breakdown for the Upgrade

The total expense varies depending on whether you are converting an originally returnless system (like most factory LS cars) or replacing an existing aftermarket regulator. Below is a detailed estimate for a typical LS swap:

Item Estimated Cost (USD)
Aeromotive Stealth Regulator (13136) $150 – $200
Fuel rail adapter or remote mount kit (if needed) $30 – $80
-6 AN return line (10 feet braided hose + fittings) $50 – $120
-8 AN supply line (10 feet + fittings) $60 – $140
Fuel pump upgrade (Walbro 450 or similar) $100 – $200
Fuel pressure gauge (liquid-filled) $20 – $50
AN wrenches, thread sealant, misc hardware $15 – $40
Total (basic installation, DIY) $425 – $830

Professional installation adds labor: figure 3–6 hours at $100–$150 per hour, adding $300–$900. However, most LS builders save money by plumbing the system themselves. Budget an additional $100 if you need a new fuel tank sump or fuel cell return port.

Tuning Considerations and Pressure Adjustments

Once the Aeromotive Stealth is installed, you must inform your ECU tuner about the new pressure settings. The airflow model in the tune relies on a known base pressure. Changing from 58 psi (factory) to a different value (e.g., 43.5 psi for some injectors) will skew the injector flow rate table. Most tuners will recommend setting the pressure to match the injectors' rated pressure (commonly 43.5 psi or 58 psi).

For boosted LS engines, the Stealth includes a vacuum/boost reference port. Connect a hose from that port to the intake manifold. This allows the regulator to increase fuel pressure 1:1 with boost, maintaining a constant differential across the injectors. Without this reference, fuel pressure would drop under boost, causing lean misfires. Verify the regulator's boost reference works correctly by checking the gauge at idle (vacuum lowers pressure 5–10 psi) and under boost (pressure rises accordingly).

Common Pitfalls and Solutions

Even experienced builders encounter issues. Here are the most frequent problems and how to avoid them:

  • Fuel smell or drip at the regulator base: Often caused by over-tightening the AN fittings, which damages the O-rings. Replace the sealing washers and lubricate with fuel-compatible oil before reinstalling. Also check that the regulator's cap screws are snug (but not stripped).
  • Pressure reads higher than set after pump primes: This is normal due to no flow—the bypass valve requires fuel flow to regulate. After starting the engine, pressure should drop to the set point. If it remains high, check for a blocked return line or a collapsed hose.
  • Whining noise from the regulator: Aeromotive Stealth units are nearly silent when functioning properly. A whine usually indicates the piston is vibrating against the body, often from air in the fuel or a too-stiff spring. Bleed the system by momentarily opening a test port and let the pump run for 30 seconds to purge air.
  • Pressure drifts when engine warms up: Ethanol fuels expand with heat, causing pressure to rise slightly (2–3 psi). This is normal. If drift exceeds 5 psi, the diaphragm may be damaged or the regulator may be mounted too close to a heat source like a turbo manifold.

Maintenance and Longevity

The Aeromotive Stealth requires minimal maintenance. Every 12 months or 10,000 miles, inspect the fuel filter to ensure no debris reached the regulator. If you run E85, check the diaphragm condition annually—ethanol can cause premature wear on non-stainless components, but Aeromotive's unit is rated for E85 use. Replace the O-rings and sealing washers every time you remove the regulator.

Keep the small vent hole on the cap clean. If it becomes clogged with dirt or oil, the regulator may not adjust correctly. A short length of small-diameter vacuum hose routed to a dry location can help keep it clear.

Where to Buy and External Resources

For best pricing and availability, purchase directly from Aeromotive's official site or reputable speed shops like Summit Racing and Jegs. For detailed LS-specific wiring and pump relay upgrades, consult the technical articles on LS1Tech, a proven resource for LS engine builders. A video walkthrough of the installation can be found on this YouTube tutorial (update with a real link if needed).

Conclusion

The Aeromotive Stealth Fuel Pressure Regulator delivers reliable, adjustable fuel pressure for Chevy LS engines in a compact package that simplifies engine bay layout. Whether building a naturally aspirated street car or a 1,000-horsepower turbocharged beast, this regulator provides the flow capacity and precision needed for safe tuning. The installation is a day's work for a competent DIYer, and the cost—typically under $1,000 for the whole system—is a smart investment to protect your engine from lean fuel conditions. Pay attention to the details: clean fittings, proper vacuum reference, and a quality fuel pump will ensure years of trouble-free operation.