BOV vs Wastegate: What's the Difference and Do You Need Both?
Both parts release pressure from a turbocharged system, which is exactly why they get lumped together — but they're solving two different problems that happen to sound similar from the outside.
A wastegate controls boost pressure on the exhaust side, bypassing exhaust gas around the turbine to prevent overboost during normal operation — it's always active and working. A blow off valve operates on the intake side, releasing built-up pressure specifically when the throttle closes suddenly, preventing compressor surge. Most turbocharged vehicles use both, because they handle different moments in the boost cycle.
Grundig Universal 38mm BOV
Billet aluminum body, hand-matched piston, tested for proper sealing before it ships. The dual-port design lets you run it MAF-compatible and recirculating, or convert it to vent-to-atmosphere with the included trumpet — one valve, either setup.
Two different jobs, two different sides of the turbo
| Wastegate | Blow Off Valve | |
|---|---|---|
| Location | Exhaust side, controls turbine spin | Intake side, on the charge piping |
| When it activates | Continuously, regulating boost during acceleration | Momentarily, when the throttle closes suddenly |
| What it prevents | Overboost / excessive turbine speed | Compressor surge from a suddenly closed throttle |
| Is it required? | Yes, on virtually every turbocharged engine | Often included stock, but frequently upgraded aftermarket |
Why they're often confused
Both involve "releasing pressure" from a system most drivers don't think about in detail, and both can be heard or felt during hard acceleration, which blurs the line for a lot of people learning about forced induction for the first time. The distinction that actually matters: a wastegate is working the entire time you're building boost, keeping it from climbing too high. A BOV only does something in that specific moment right after you lift off the throttle — it has nothing to do with regulating boost while you're accelerating.
Do you need to upgrade both?
- Wastegate upgrades matter most when you're increasing boost beyond what the factory wastegate is sized to control — a common step alongside other performance upgrades, but not something most stock or mildly modified engines need to touch.
- BOV upgrades are more commonly done independently — often for improved response, sound, or reliability compared to a factory diverter valve, without needing any change to boost levels at all.
Simple way to remember it: the wastegate manages how much boost you build. The blow off valve manages what happens to that boost the instant you stop asking for it.
If you're exploring upgrades to either system, it's worth looking at your wastegate options and blow off valve lineup separately, since they're addressing different parts of the boost system and rarely need to be changed together unless you're significantly increasing overall boost pressure.
Internal vs external wastegates
Wastegates come in two broad designs. An internal wastegate is built directly into the turbo's turbine housing — compact and factory-common, but limited in how much exhaust flow it can bypass, which becomes a ceiling on how much boost it can effectively control at higher power levels. An external wastegate is a separate unit plumbed into the exhaust system before the turbine, offering more bypass capacity and generally more precise control — which is why it's the common upgrade path when significantly increasing boost beyond what a factory internal wastegate is sized to manage.
Boost creep: what happens when a wastegate can't keep up
"Boost creep" describes boost pressure climbing beyond its target as RPM increases, because the wastegate physically can't flow enough exhaust gas around the turbine to hold the pressure where it's supposed to be. This is a wastegate sizing problem specifically — it has nothing to do with the blow off valve, even though both terms get thrown around in the same performance conversations. If boost is climbing higher than intended at higher RPM, the wastegate (its size, spring, or actuator) is where to look, not the BOV.
How the ECU factors in on modern setups
On most modern turbocharged engines, the wastegate's actuator is controlled electronically via a boost control solenoid, which the ECU modulates based on real-time conditions rather than relying purely on a fixed mechanical spring pressure. This allows more precise, responsive boost control than older purely mechanical wastegate actuators — but it also means wastegate behavior on these engines is partly a tuning question, not just a hardware question, which is part of why aftermarket wastegate upgrades are frequently paired with a supporting tune.
FAQ
Can I install a blow off valve without upgrading the wastegate?
Yes — these are independent components addressing different parts of the boost system, and BOV upgrades are commonly done on their own without any change to boost levels or wastegate function.
Does a wastegate make the same sound as a blow off valve?
No, a wastegate operates continuously and quietly during boost buildup on most setups, while the "psshh" sound associated with forced induction typically comes from a blow off valve venting on throttle lift.
Do all turbocharged cars have both a wastegate and a BOV?
Virtually all have a wastegate, since it's essential for controlling boost. Most also have some form of diverter or blow off valve stock, though it's frequently one of the first parts owners choose to upgrade.
If I increase boost, do I need to upgrade both parts?
Often the wastegate is the more critical one to reassess, since it needs to be sized to control the new boost level. The BOV usually doesn't need to change purely because boost increased, unless it was already marginal for the airflow being handled.