What Does A Blow Off Valve Do And How Does It Affect Your Car's Performance?

Often a topic amongst car modders, the blow-off valve has both its die-hard fans and its detractors. With such strong opinions flying around, you may wonder where exactly you fall on the spectrum. Debate rages about the usefulness and desirability of this part. Do blow-off valves decrease performance? Do blow-off valves increase performance? Is it a necessary mod or a waste of time and money?

To answer all these questions, let’s break down exactly what this valve is, what it does, and whether it will affect your turbocharged vehicle’s performance. 

Turbo-boosted engines and diverter valves

A blow-off valve is a type of diverter or bypass valve, which all modern turbocharged engines need, but it’s not the basic model. 

The basic principles at play with a turbo engine are this: a turbocharged system gives you extra power by forcing extra air into the cylinders, creating a more explosive moment at the point of combustion, which can boost performance. The problem with this system is that lift during a turbo boost can cause the engine to surge. This produces the sound known as ‘turbo flutter’, and while some revheads may love it, it’s not a good sign for the engine's health.

Diverter valves work by quickly capturing and recirculating (hence, ‘recirc’) excess air from a turbo boost to balance the air pressure and risk damage to the engine. It protects the engine from surge conditions and keeps things balanced in milliseconds. However, standard diverter valves have also won a reputation for being a bit of a joy kill, especially when it comes to the addictive revving and turbo-boosted sounds we know and love. 

What does a blow-off valve do?

This is where the blow-off valve gets its moment to shine. Designed to be a solution to compressor surge, the blow valve is only required to be attached at one end and fits closely to the throttle body in between the throttle and the turbo, ready to respond to any surge situation that comes its way. It quickly exhausts any excess air in the system. 

Ask a turbo driver, “what does a blow-off valve do?” and they might tell you that it makes an awesome hissing or whooshing noise. It’s become one of the dump valve’s defining features and offers a pleasing alternative to the buzz kill of the standard diverter valve. 

The sound might be part of the appeal, depending on your preference. Still, ultimately the blow-off valve can quickly divert excess air during turbo-boosting and its ability to avoid compressor surge is its real function.

Does a blow-off valve affect performance?  

Simply put, the answer to this question is no. The myth that blow-off valves decrease performance may have been caused by the spring pre-load being adjusted too tightly. Doing so can cause compressor surge and turbo flutter, but it isn’t down to the valve itself. With a properly fitted blow-off valve, you’ll find you get better performance and longevity from your turbo engine and protect it in the long run. 

Car Mods Australia — the home of turbo superchargers, blow-off valves and more

At Car Mods Australia, we’ve got all the turbo and car supercharger gear you could ever want. Shop our range of blow-off valves, wastegates, turbo mods, turbo kits, actuators and BOV adapters today, and discover why more turbo enthusiasts choose us. Need help finding the right blow-off valve for your vehicle? Talk to us and we’ll help you out.