A blow off valve (BOV) releases pressurized air from the intake system when the throttle plate closes. This prevents compressor surge, which can damage the turbocharger. Setting the BOV correctly is crucial for optimal performance and turbo health. Improperly adjusted BOVs can lead to issues like compressor surge or poor engine performance. This guide explains How To Set A Blow Off Valve to avoid these problems.
Understanding Compressor Surge and BOV Function
Compressor surge occurs when the throttle closes abruptly, forcing pressurized air back into the turbocharger compressor wheel. This reversal of airflow can cause significant damage, ranging from excessive shaft load on bearings to a catastrophic turbine shaft failure. The BOV vents this excess pressure, protecting the turbo. Symptoms of compressor surge include a distinctive fluttering or “chugging” sound and potentially reduced performance.
Types of Blow Off Valves
Different BOV designs operate with varying mechanisms and pressure sensitivities:
- Plunger-Style BOVs: These utilize a spring-loaded plunger to seal against pressure. They are known to leak at certain PSI levels, depending on the spring and overall design. The leak point, where the valve begins to release pressure, is crucial for proper operation.
- Pull-Type BOVs: These valves utilize a diaphragm or piston pulled open by vacuum. They tend to be more responsive and hold higher boost pressures more effectively than push-type valves.
- Push-Type BOVs: These valves use pressure to open against a spring. These are less common than pull-type due to potential issues with premature opening at high boost levels.
Setting the BOV
The specific adjustment method varies depending on the BOV type. However, the fundamental principle remains consistent: finding the optimal balance between preventing compressor surge and minimizing unnecessary venting.
For adjustable BOVs:
- Start with the manufacturer’s recommended setting. This provides a safe baseline for initial adjustment.
- Adjust the spring tension or preload. Increasing tension typically raises the pressure at which the valve opens.
- Fine-tune based on driving conditions and boost levels. Monitor for signs of compressor surge during hard acceleration and deceleration. If surge is present, increase the spring tension slightly. If the valve vents too frequently under light throttle conditions, decrease the tension.
General Guidelines:
- Prioritize preventing compressor surge over maximizing venting sound. While the distinctive “whoosh” of a BOV can be appealing, protecting the turbocharger is paramount.
- Consider using a boost gauge for accurate adjustments. Monitoring boost pressure allows for more precise BOV setting, ensuring optimal performance and turbo protection.
- Consult a professional tuner if you are unsure about the adjustment process. Incorrect settings can negatively impact performance and turbo longevity.
Conclusion
Properly setting a blow off valve is vital for safeguarding your turbocharger from the damaging effects of compressor surge. By understanding the function of a BOV and following the appropriate adjustment procedures, you can ensure optimal performance and longevity for your turbocharged engine. Remember to always prioritize preventing compressor surge over achieving a specific sound. When in doubt, consult with a qualified tuner for expert guidance.
