Blow off Valve’s

Blow off valve’s

A blow off valve (Also named BOV or dumpvalve) is used to release boost from a turbo or superchargersystem when it’s not used(switching gears, releasing throttle). A blow off valve is a valve that’s installed on the pressure hoses and uses a signal(electronic or vacuum) to open. At that time the air vents out creating the familiar blow off sound.

A blow off valve can be installed on over 98% of all turbo petrol cars and also on most diesel engines there are possibilities to create this sound. To view if we already offer a kit for your engine click here! If you can’t find a set for your car please read further or contact us!

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Why a blow off valve?

A turbo reaches very high rotations (Up to 200.000 rpm and over) so when it’s spooled up for usage it will take some time to drop back down in rpm. If the turbo is spooled up and the throttle valve closes the turbo will build up a huge amount of pressure in an extremely short amount of time. This pressure can be so high it ruptures hoses but it is even capable of destroying the turbo’s impeller wheel. If that happens and the parts from the impeller get sucked into the engine it can even destroy the complete engine.

To prevent this from happening most turbo petrol engines are equipped with a recirculation (bypass) valve or blow off valve. Most of these work on a difference in pressure between the intake manifold and the pressure hoses. If the difference rises (For instance, releasing the throttle or changing gears) the valve is opened and the turbo is protected.

A second benefit of a blow off valve is that due to releasing the pressure from the hoses the turbo notices less resistance and will stay better spooled up. This makes sure that when changing up in gears the turbo will respond better afterwards and lag is reduced resulting in a better acceleration.

Pros and cons

As previously mentioned is a blow off valve or recirculation valve very important for the durability of the turbo and reducing lag. Another benefit specifically for the blow off valve is that as it vents the pressure into the atmosphere it also removes a lot of heat from the system which would otherwise be circulated back. Less heat means more power! The blow off sound is offcourse also important for enhancing the turbo car experience.

Mechanically there are almost no downsides for installing a blow off valve, unfortunately this doesn’t mean a blow off valve can be installed on any car without problems. The original engine management often uses a air flow meter to calculate the amount of air getting sucked into the engine to better calculate the amount of fuel needed. If a blow off valve is installed after this sensor, the air flow metre will registre air that should go into the engine but when it get’s vented out it will register an error code. This doesn’t mean that a blow off valve is not possible on these engines as the sensibility differs per engine and ECU. In most cases these errors can be prevented by only partially venting the air and recirculating the other part. To get this to work you could choose for keeping the original recirculation valve installed besides the blow off valve but there are also specially designed semi-open blow off valves available.

Recirculation valve

From the factory most turbo petrol cars are equipped with a bypass- or recirculation valve. These valves work similar to a blow off valve but in stead of venting into the atmosphere the excess pressure is blown back into the intake pipe. On many engines there is a possibility to swap this valve for a blow off valve that vents into the atmosphere, for other models there are adapters available to turn them into blow off valve’s. In all other cases there will have to be made a new connection to get the blow off valve installed. For several models there are also blanking plugs available to completely block off the original recirculation valve connection.

We have these recirculation valves in 25mm and 32mm in our range.

Diesel dumpvalves

Most diesel engines don’t have a throttle valve, when shifting gears the excess pressure is blown out through the engine and exhaust. Installing a blow off valve won’t have any effect on the performance or life span of the turbo. There are sets available to get the blow off sound from these engines. These kits work by utilising the throttle pedal signal and electronically open a valve when the throttle is released.

At chargertech we offer 2 different sets for this application. Type 1 uses the electronic gas pedal signal (0-5V) and decides on a sufficient amount of throttle release to shortly open the valve. Type 2 works with a switch behind the throttle pedal. If the pedal is released this system will also give a signal to open the blow off valve..

If the throttle signal fals within the above mentioned range we always suggest to use the first type. The second model is suited for all other applications.

Installing a diesel dumpvalve is not completely without risks. The air that flows out through the dumpvalve can be seen by the ECU as a leak resulting in errors. A dumpvalve that stays open for to long can also result in extra wear and tear on the turbo as it will spin more rapidly. It’s always advised to check this after installation and never make the spring pressure to low.