Subaru TGV Delete: Unlock Hidden Power in Your EJ Engine

Ever felt your Subaru could deliver more punch? You’re probably right. Hidden beneath your intake manifold lies a restrictive component that’s holding back your engine’s true potential. A TGV delete might be exactly what you need to unleash those extra horses.

What Are Subaru TGVs and Why Would You Delete Them?

TGVs (Tumble Generator Valves) are butterfly valve assemblies sitting between your intake manifold and cylinder heads. They’re designed to improve cold-start emissions by creating air “tumble” when the engine is cold.

Here’s the problem: even when fully open, TGVs restrict airflow with their center divider plates. This creates a bottleneck that limits your engine’s breathing capacity at higher RPMs.

Removing these restrictors:

• Creates unrestricted airflow into your cylinders
• Increases horsepower (typically 10-20hp with proper tuning)
• Improves throttle response
• Reduces torque dips during warm-up phases

As reported by numerous Subaru enthusiasts, the power difference is noticeable, especially at higher RPMs where airflow matters most.

TGV Delete Options: DIY vs. Aftermarket Kits

You’ve got several routes to TGV freedom:

DIY Cut-and-Grind Method

This budget-friendly approach involves physically removing the butterfly plates while keeping the original housings.

Pros:

• Minimal cost (just basic tools)
• Retains OEM part numbers
• No need to purchase additional hardware

Cons:

• Time-consuming (3-5 hours for beginners)
• Requires careful removal of peened Phillips screws
• Potential for rough interior finish

Aftermarket Delete Kits

These professionally manufactured solutions come in different styles:

Plug Kits: Use set screws and JB Weld to seal shaft holes after butterfly removal.

• Mid-range cost ($50-80)
• SW Speed Co. offers popular 3D-printed options

CNC-Machined Billet Housings: Complete replacement units with smooth interior passages.

• Premium option ($49-150)
• BLOX Racing’s 5-axis TGV delete kits feature perfect smoothness
• IAG Performance V3 housings include optional butterfly pass-through for emissions testing

Complete Step-by-Step TGV Delete Guide

Required Tools:

• Socket set and wrenches
• Screwdrivers
• Drill or reciprocating saw (for screw removal)
• Die grinder or Dremel (for porting)
• Brass punch and hammer (shaft removal)
• Thread tap set (if using set screw method)
• JB Weld or similar epoxy
• New intake manifold gaskets

1. Preparation and Access

Start by disconnecting your battery and removing components blocking access to your intake manifold:

• Intercooler piping
• Intake system
• Any accessories or covers

Next, remove the intake manifold to expose the TGV assemblies. Keep track of all bolts and their locations!

2. TGV Motor Removal

The electrical motors that control TGV operation must be carefully preserved:

• Remove the 10mm bolts securing each motor
• Gently extract the motors, noting their orientation
• Store them safely with their O-rings intact

3. Butterfly Plate Extraction

This is the trickiest part of the process:

• Locate the Phillips screws securing the butterfly plates
• These are typically peened (mechanically locked), making conventional removal difficult
• Use a drill or reciprocating saw to cut off screw heads
• Extract remaining screws from the shaft
• Slide out the butterfly plates and center dividers

As documented in detailed tutorials, patience is crucial during this step.

4. Shaft Removal

With the butterflies gone, you’ll need to remove the shafts:

• Position a brass punch against the end of the shaft (opposite the plastic gear)
• Carefully tap the shaft out with a hammer
• Remove any remaining components or debris

5. Port and Polish (Optional but Recommended)

Smoothing the internal passages maximizes airflow benefits:

• Use a carbide bit on a die grinder for rough shaping
• Follow with a Dremel and Scotch-Brite for final polishing
• Focus on removing sharp edges and creating smooth transitions
• Maintain some surface texture for fuel atomization

6. Plugging Shaft Holes (For DIY Method)

If you’re keeping the OEM housings:

• Tap the shaft holes to 3/8″-16 thread size
• Insert appropriate set screws with JB Weld
• Once cured, grind flush with housing surface

Popular DIY tutorials show this process in detail.

7. Reassembly

With modifications complete:

• Reinstall TGV motors with their O-rings
• If using aftermarket housings, follow their specific instructions
• Replace intake manifold with new gaskets
• Reconnect all sensors, hoses, and accessories
• Reinstall intake system and intercooler piping

The Check Engine Light Situation

Here’s the catch: removing TGVs will trigger a Check Engine Light (CEL) because the ECU detects the butterfly plates aren’t moving. You have two options:

Mandatory ECU Tuning

The proper solution is a custom ECU tune that:

• Disables TGV-related fault codes
• Adjusts fuel maps for increased airflow
• Optimizes timing for your new setup

Temporary Code Clearing (Not Recommended)

Some owners attempt to clear codes using scan tools, but this is a short-term fix. As discussed in Subaru forums, the ECU will eventually recheck TGV operation and throw codes again.

Aftermarket TGV Delete Kit Comparison

CNC Innovations and RCA Garage also offer quality options with differing features and price points.

Real-World Performance Impact

What can you actually expect from a TGV delete?

The consensus among tuners and enthusiasts is a gain of 10-20 horsepower, with most of that improvement coming in the mid to high RPM range. Additionally, many drivers report:

• Improved throttle response
• Smoother power delivery
• Elimination of dips in the power curve
• Better engine sound (slightly deeper intake tone)

Emissions and Legal Considerations

It’s important to address this head-on: TGV deletes violate emissions regulations in many jurisdictions. The TGV system is part of your vehicle’s emissions control equipment, and tampering with it:

• May violate federal and state emissions laws
• Could potentially affect vehicle inspection/registration in emissions-testing regions
• Is technically intended for off-road or racing use only

Some companies like IAG offer removable butterfly systems that can be reinstalled for emissions testing, but this approach still raises legal questions.

Installation Tips for Success

Save yourself headaches by following these proven tips:

1. Take photos before disassembly – document everything for reference during reassembly
2. Label all vacuum lines – mix-ups can cause running issues
3. Use anti-seize compound on all bolts going into aluminum
4. Replace all gaskets – never reuse old intake gaskets
5. Have a tuner lined up before installation
6. Don’t rush the process – this is a 3-5 hour job for most DIYers

Combining TGV Delete with Other Mods

TGV deletes work exceptionally well when paired with:

• Equal Length Headers – maximize exhaust flow to match intake improvements
• Upgraded Intercooler – handle the additional airflow with better cooling
• Electronic Boost Controller – take advantage of improved flow with proper boost management
• Upgraded Fuel System – ensure adequate fuel delivery for increased airflow

As BLOX Racing explains, these mods create a synergistic effect when properly tuned together.

Is a Subaru TGV Delete Right for You?

This modification makes the most sense if:

• You’re already planning to get a custom ECU tune
• You’re pursuing maximum performance from your EJ engine
• You use your Subaru primarily for track days, autocross, or off-road
• You understand and accept the emissions implications

If you’re keeping your car completely stock and street-legal, this might not be the right modification path.

Final Thoughts on TGV Deletes

Removing the restrictive TGV assembly is one of the most cost-effective power mods available for EJ-engine Subarus. For $50-150 and a few hours of work, you can unlock significant horsepower that the factory left on the table.

Just remember: proper tuning isn’t optional—it’s mandatory for both performance gains and preventing check engine lights. When done correctly, a TGV delete transforms your Subaru’s intake flow, contributing to that addictive boxer rumble and push-you-back-in-your-seat acceleration we all love.