How To Adjust Blow Off Valve

So, you're wondering how to adjust your blow off valve (BOV)? You've come to the right place. A blow off valve is a crucial component in a turbocharged engine, designed to release excess pressure when you let off the throttle. Adjusting it correctly can optimize performance and prevent damage to your turbocharger. This guide will walk you through the process, covering everything from understanding why it matters to troubleshooting common issues.

Why Adjusting Your Blow Off Valve Matters

The primary purpose of a blow off valve is to relieve pressure buildup in the intake system when the throttle closes. When you accelerate in a turbocharged car, the turbocharger spins rapidly to force more air into the engine. When you suddenly release the accelerator, the throttle plate slams shut, blocking the airflow. The turbocharger, however, is still spinning and creating pressure. Without a way to vent this excess pressure, it can cause several problems:

Compressor Surge: This is the most significant concern. The pressurized air has nowhere to go, so it reverses direction and slams back against the turbocharger's impeller. This creates a "fluttering" or "chirping" noise and can severely damage the turbocharger over time.
Reduced Turbocharger Lifespan: Repeated compressor surge puts immense stress on the turbocharger's bearings and seals, significantly shortening its lifespan.
Poor Throttle Response: The pressure buildup can hinder the turbocharger's ability to spool up quickly when you get back on the throttle, resulting in lag and reduced performance.
Potential for Boost Creep: While less common, improper BOV function can contribute to boost creep, where the boost pressure exceeds the intended level.

Properly adjusting your BOV ensures that it releases the pressure quickly and efficiently, preventing these issues and maximizing performance. A well-adjusted BOV contributes to a smoother driving experience and protects your turbocharger from premature wear and tear.

How to Choose the Right Blow Off Valve for Your Needs

Before you start adjusting, it's essential to ensure you have the right type of blow off valve for your application. There are two main types of BOVs:

Vent-to-Atmosphere (VTA) BOVs: These valves vent the excess pressure directly into the atmosphere, creating the distinctive "whoosh" sound. VTA BOVs are generally simpler to install and adjust, but they can cause issues with some vehicles that rely on a mass airflow sensor (MAF). VTA BOVs vent metered air to the atmosphere which can cause the engine to run rich after the throttle is closed.
Recirculating BOVs: These valves recirculate the excess pressure back into the intake system before the turbocharger. Recirculating BOVs are generally recommended for vehicles with MAF sensors because they prevent unmetered air from entering the system, which helps maintain proper air-fuel ratios.

When choosing a BOV, consider the following factors:

Vehicle Type: As mentioned, vehicles with MAF sensors generally benefit from recirculating BOVs, while vehicles with speed density systems are often compatible with VTA BOVs. Consult your vehicle's service manual or a trusted mechanic to determine which type is best for your application.
Boost Level: Higher boost levels require a more robust BOV capable of handling the increased pressure. Look for BOVs specifically designed for your target boost range.
Flow Capacity: The BOV's flow capacity should match the output of your turbocharger. A BOV that is too small will not be able to release the pressure quickly enough, defeating its purpose.
Build Quality: Choose a BOV from a reputable manufacturer known for using high-quality materials and precise machining. This will ensure reliability and longevity.

Once you've selected the right BOV, you can proceed with the adjustment process.

How to Adjust Your Blow Off Valve: A Step-by-Step Guide

The adjustment procedure varies slightly depending on the BOV model, but the general principles remain the same. Always refer to the manufacturer's instructions for specific details.

Locate the Adjustment Screw: Most BOVs have an adjustment screw or knob that controls the spring tension. This screw is typically located on the top or side of the valve.
Start with a Baseline Setting: Begin with the spring tension relatively loose. This will allow the valve to open easily. For a VTA BOV, this might mean the valve is slightly open at idle. For a recirculating valve, it should be closed at idle.
Test Drive and Listen: Take the vehicle for a test drive and pay attention to the sound of the BOV. Listen for compressor surge, which sounds like a fluttering or chirping noise coming from the turbocharger when you release the throttle.
Adjust the Spring Tension: If you hear compressor surge, increase the spring tension by tightening the adjustment screw in small increments (e.g., a quarter turn at a time). After each adjustment, take the vehicle for another test drive to see if the surge has disappeared.
Repeat the Process: Continue adjusting the spring tension until the compressor surge is eliminated. The goal is to find the minimum spring tension required to prevent surge. Too much spring tension can make the valve sluggish to open, which can also negatively impact performance.
Check for Other Issues: Once you've eliminated compressor surge, pay attention to how the engine behaves under different driving conditions. Look for signs of hesitation, poor throttle response, or boost leaks. These issues may indicate that the BOV is not functioning correctly.
Fine-Tune as Needed: Adjustments are best made over several drives to see how the BOV behaves in various situations. Consider keeping a log of your adjustments and the results to make fine-tuning easier.

Important Considerations:

Vacuum Leaks: Ensure there are no vacuum leaks in the BOV's vacuum line. A leak can cause the valve to open prematurely or not open at all.
BOV Placement: The placement of the BOV can also affect its performance. Ideally, the BOV should be located as close to the throttle body as possible.
Professional Help: If you are unsure about any aspect of the adjustment process, it's always best to seek the assistance of a qualified mechanic.

Real-World Owner Experiences: Tips and Troubleshooting

Many owners have shared their experiences adjusting BOVs, offering valuable insights and troubleshooting tips:

"Start Slow": As mentioned earlier, start with a loose spring tension and gradually increase it. Over-tightening the spring can cause other problems.
"Listen Carefully": Pay close attention to the sounds coming from your turbocharger. The presence or absence of compressor surge is the best indicator of proper adjustment.
"Check Your Plugs": If you are running a VTA BOV on a vehicle with a MAF sensor, check your spark plugs for signs of running rich. This is more likely when you are not running an aftermarket tune.
"Vacuum Line Integrity": One owner reported persistent compressor surge even after multiple adjustments. It turned out that the vacuum line to the BOV was cracked, causing it to leak. Replacing the line solved the problem.
"Consult Online Forums": Many online forums dedicated to specific car models have threads discussing BOV adjustments. These forums can be a valuable resource for finding model-specific advice and troubleshooting tips.

Frequently Asked Questions (FAQs)

Here are some frequently asked questions about adjusting blow off valves:

Q: What happens if my BOV is too loose?

A: A BOV that is too loose will open prematurely, causing a loss of boost pressure. This can result in poor throttle response and reduced performance.

Q: What happens if my BOV is too tight?

A: A BOV that is too tight may not open quickly enough or at all, leading to compressor surge. This can damage your turbocharger.

Q: Can I adjust my BOV without a boost gauge?

A: While a boost gauge can be helpful, it's not strictly necessary. You can adjust the BOV by listening for compressor surge and observing the engine's behavior. However, a boost gauge will allow for more accurate adjustment and provide valuable information about boost pressure.

Q: How often should I adjust my BOV?

A: Once properly adjusted, a BOV typically doesn't require frequent adjustments. However, it's a good idea to check its function periodically, especially if you notice any changes in the engine's performance or the sound of the BOV.

Q: Are aftermarket tunes required to run an aftermarket BOV?

A: Not all applications require an aftermarket tune. However, running a VTA BOV with a MAF sensor can often cause issues that require a proper tune to address. Consult with a tuner to determine the best solution for your setup.

By following these guidelines and understanding the principles involved, you can effectively adjust your blow off valve to optimize performance, protect your turbocharger, and enjoy a smoother driving experience. Remember to consult your vehicle's service manual and the BOV manufacturer's instructions for specific details. Good luck, and happy tuning!