When upgrading your turbocharged vehicle, understanding the difference between a blow off valve (BOV) and a diverter valve (DV) is crucial. Both manage excess pressure from the turbo, but they do so in distinct ways, impacting performance and sound. This guide breaks down the key differences between BOVs and DVs to help you choose the right one for your car.
How a Diverter Valve Works
In a turbocharged engine, the throttle plate opens when you accelerate, allowing air to be compressed and forced into the engine by the turbocharger. When you shift gears and lift off the throttle, the throttle plate closes. However, the turbo continues spinning, creating pressurized air that needs to be managed.
A diverter valve recirculates this pressurized air back into the intake system before the turbocharger. This prevents the turbo from experiencing abrupt deceleration and potential damage. By recirculating the air, the mass airflow sensor (MAF) accurately measures the air volume, ensuring proper fuel delivery and a smooth running engine.
Aftermarket diverter valves often offer improved performance over stock valves by handling higher boost pressures more efficiently and minimizing turbo lag.
Blow Off Valves Vent to Atmosphere
Unlike diverter valves, blow off valves release excess pressure into the atmosphere, creating the distinctive “whoosh” or “pshh” sound often associated with turbocharged cars.
While the sound can be appealing, venting pressurized air can disrupt the engine’s air/fuel ratio. This is because the MAF sensor has already measured the air that’s now being vented, potentially leading to a momentarily rich fuel mixture. In some vehicles with sophisticated engine management systems, this can trigger error codes or drivability issues.
Diverter Valve Benefits: Performance and Reliability
Factory-equipped diverter valves play a critical role in regulating turbocharger boost pressure. They ensure smooth operation across various engine conditions, from idle to full throttle. A malfunctioning or inadequate diverter valve can cause boost leaks, increased turbo lag, and sluggish throttle response.
Upgrading to an aftermarket diverter valve can improve performance, especially in tuned or modified vehicles with higher boost levels. Aftermarket DVs are often designed to handle increased pressure more effectively, providing better throttle response and reducing turbo lag. They’re especially important for vehicles with performance chips or tunes, as increased boost can put extra strain on the stock diverter valve.
Choosing the Right Valve: BOV vs. DV
The key difference lies in where the excess air goes: recirculated back into the intake (DV) or vented to the atmosphere (BOV). Diverter valves maintain a more consistent air/fuel ratio and are generally recommended for most vehicles, especially those with sensitive engine management systems. Blow off valves offer a distinctive sound but can potentially cause issues with fuel delivery and engine performance. Your choice ultimately depends on your performance goals, desired sound, and vehicle compatibility. If you’re unsure which valve is right for your car, consult with a qualified mechanic or performance tuning specialist.
Installing an Aftermarket Diverter Valve on a Volkswagen or Audi 1.8T
The factory diverter valve on a 1.8T engine is typically located on the side of the turbocharger’s compressor housing, often tucked between the passenger-side fender well and firewall. Replacing it with an aftermarket valve involves removing three Allen bolts and installing the new valve. A lift is recommended for easier access. Upgrading to a more robust aftermarket diverter valve can address potential boost leaks and improve reliability, especially in tuned vehicles. Always consult a repair manual or professional for specific instructions related to your vehicle.
