Turbocharged vehicles are becoming increasingly common. A smaller turbocharged engine is not only more powerful, but it also allows for more tuning options. We sometimes see people on forums who are unsure what a bypass valve (BPV) is and how it differs from a blow-off valve (BOV).
What Is A Blow Off Valve/ Electronic Boost Bypass Valve?
When forced induction is used in an engine, a way to release the pressurized air when the throttle body is closed is needed. When the throttle body closes and there isn't a way for the air to exit, pressure will build up and push air into the turbocharger in the wrong direction. This problem has the potential to completely kill your engine, turbocharger, and other components.
A Blow Off Valve/electronic boost bypass valve solves this problem by allowing pressurized air to escape from the inlet tubing while simultaneously measuring the manifold pressure. The relative manifold pressure decreases below atmospheric pressure when the throttle body closes. The valve opens when the pressure drops, allowing the excess pressure to escape. It helps the valve to sense when the pressure changes and become operational by piping manifold pressure to it.
Blow Off Valve
If the vehicle has a manual transmission, this can be very annoying in between gears, particularly on a racetrack or canyon road where throttle modulation is needed.
If a BOV releases all of the remaining pressure into the atmosphere, boost pressure must be reset to zero. When you're changing and you're experiencing turbocharger lag in every gear, this can be extremely frustrating.
Since they normally don't have anywhere to recirculate the air, racing applications will vent it completely to the atmosphere. They also don't need to recirculate the air because they're all speed-density calibrated, so metering the air back into the intake is unnecessary. It's quick and easy to use this device.
Another issue with a BOV is that the air being vented was previously determined by a mass airflow sensor. Since the air is vented after it has been weighed, your car can run extremely rich during changes. This is why, in between moves, cars with forced induction will sometimes cough out black smoke. Fortunately, this is a problem that can be resolved with a little tweaking.
Electronic Boost Bypass Valve
An electronic boost bypass valve differs from a blow-off valve in that it does not allow air to escape to the atmosphere. Instead, before the turbo or supercharger inlet, but after the airflow sensor, it recirculates the air back into the chamber. This design maintains a more consistent strain. Furthermore, by reintroducing air after the sensor, any tuning problems can be avoided.
A recirculation valve is typically a bypass valve. This ensures that the boost pressure you're breathing is recirculated back into the airbox or elsewhere in the intake system. The bypass valve, on the other hand, isn't perfect. The ability of this design to withstand high horsepower applications is a major concern.
Should You Upgrade From An Electronic Boost Bypass Valve To A Blow Off Valve?
You may be wondering if it's worthwhile to upgrade from anelectronic boost bypass valve to a blow off valve.
An aftermarket electronic boost bypass valve can flow more air more reliably than the factory plastic bypass valve. There is no need to turn to a 100% vent-to-atmosphere blow-off valve before you upgrade from the factory turbocharger and begin to upgrade beyond the capabilities of a bypass valve.
When it comes to a car, it all comes down to horsepower and personal preference–or if you want to wake up the whole city on your way to Coffee. On a racing car, the solution is obvious–you can just consider a blow-off valve.
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