Adjustable PCV Restrictor Valve, -6AN

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  • Adjustable PCV restrictor with 5 pre-drilled restrictor plate sizes.
  • Replace your traditional PCV valve with an adjustable restrictor for better reliability and increased crankcase vacuum.
  • Allows fine tuning the PCV airflow in your engine.
  • No moving parts for improved durability.
  • Perfect for LS engines with aftermarket valley covers that have no PCV restrictor built-in.
  • Female -6 O-ring boss ports.
  • All aluminum construction with black anodized housing.
Part # FO-06R
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Improved Racing's adjustable PCV restrictor allows fine tuning of airflow through PCV lines in recirculated systems without using a traditional PCV valve. In other words, this restrictor completely replaces your factory PCV valve. It's also perfect for LS engines with aftermarket valley covers that do not have a built-in PCV restrictor like the factory cover.

This valve can be used on its own to replace a traditional PCV valve in naturally aspirated engines. In turbocharged applications, combine it with a check valve such as part number DCV-06 or FCV-06-06 to prevent pressurizing the crankcase under boost.

The kit includes five pre-drilled restrictor plates plus a blank restrictor plate with a pilot hole for drilling your own custom hole size. Each plate is laser-marked with the restrictor hole diameter in millimeters. The 2.6 mm restrictor size is the factory restrictor size found in the valley cover of most 2004+ LS1, LS2 and LS3 engines. If using the factory valley cover, drill out the factory restrictor first. We recommend starting with the 2.6mm restrictor and moving up incrementally in size.

The restrictor housing features female -6 O-ring boss ports on each end. We offer several adapter fittings to adapt it to different AN sizes or hose barb sizes, so it will work in virtually any application.

Usage Notes

This device is for advanced users. You'll need a vacuum gauge to accurately determine the correct restrictor size to use. The goal is to generate as much crankcase vacuum as possible without maxing out your idle air control valve. You may also need to adjust your tune if the PCV flow rate changes significantly from the factory setup or your previous setup. Please see our instruction manual for more details.

Features and Benefits

  • Adjustable PCV restrictor with 5 pre-drilled sizes: 2.6mm, 3.0mm, 3.5mm, 4.0mm, 4.5mm, and a blank disc with a 1mm pilot hole for custom-drilled sizes.
  • Female -6 O-ring boss ports and be adapted to many different fitting types and sizes (male AN, hose barb, quick connect, etc).
  • All aluminum construction with black anodized housing.
  • No moving parts for improved durability over traditional PCV valves.
Part #
Improved Racing
Primary Material
6061-T6 aluminum
Type II Anodized
Fitting Angle
Connection A Type
Connection A Size
Connection A Gender
Connection B Type
Connection B Size
Connection B Gender
Maximum Operating Temperature
302°F (150°C)
Minimum Operating Temperature
-40°F (-40°C)
Maximum Operating Pressure
1000 psi (68.94 bar)
on installation only
Breather and vent lines
Fuel (in-tank)
Fuel (outside of tank)
Gauge and sensor lines
Hydraulics: low pressure (return lines)
Vacuum lines
Coolant & water lines
Other oil water and air systems
Fluid Compatibility
Air and gas
Engine oil
Ethanol-based fuels (E85+)
Ethanol/gasoline mixtures
Gear oil
Nitrous Oxide
Power Steering Fluid
Racing fuels
Transmission fluid
Standards & Certifications
Anodizing per ISO 7599
O-Ring Boss Threads per SAE J1926-3 & ASME B1.1
O-Ring Boss Threads per SAE AS5202
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