Pros & Cons Of Not Running A Bov

[paulr33]

A blowoff valve is a pressure release system present in turbocharged engines. Its purpose is to prevent compressor surge, and reduce wear on the turbocharger  and engine. Blow off valves (BOV) relieve the damaging effects of compressor "surge loading" by allowing the compressed air to vent to atmosphere[1]

A compressor bypass valve (CBV), also known as a compressor relief valve or diverter valve, is a vacuum-actuated valve designed to release pressure in the intake system of a turbocharged vehicle when the throttle is lifted or closed. This air pressure is re-circulated back into the non-pressurized end of the intake (before the turbo) but after the mass airflow sensor.

A blowoff valve, (BOV, sometimes "hooter valve", not to be confused with a bypass valve) performs the same task but releases the air into the atmosphere instead of recirculating it. The blowoff action produces a range of distinctive hissing sounds, depending on the exit design. Some blowoff valves are sold with a trumpet-shaped exit that intentionally amplifies the sound. Some turbocharged vehicle owners may purchase a blowoff valve solely for the auditory effect even when the function is not required by normal engine operation. Motor sports governed by the FIA have made it illegal to vent unmuffled blowoff valves to the atmosphere.[citation needed]

Blowoff valves are used to prevent compressor surge, a phenomenon that readily occurs when lifting off the throttle of an unvented, turbocharged engine. When the throttle plate on a turbocharged engine closes, the high pressure air in the intake system is trapped by the throttle and a pressure wave is forced back into the compressor. The compressor wheel slows rapidly and may even stall, and the driver will notice a fluttering air sound. The rapid slowing or stalling stresses the turbo and imparts severe turbo lag if the driver accelerates immediately after the surge event.

n the case where a mass airflow sensor is used and must be located prior to the blowoff valve, the engine control unit (ECU) will meter out excess fuel because the atmospherically vented air is not subtracted from the intake charge measurements. The engine then briefly operates with a fuel-rich mixture after each valve actuation.

The rich mixing can lead to hesitation or even stalling of the engine when the throttle is closed, a situation that worsens with higher boost pressures. Occasional events of this type may be only a nuisance, but frequent events can eventually foul the spark plugs and destroy the catalytic converter, as the inefficiently combusted fuel produces soot (excess carbon) and unburned fuel in the exhaust flow can produce soot in the converter and drive the converter beyond its normal operating temperature range.

One way to mitigate the problem is to reduce the boost pressure, which reduces the required venting volume and yields less charge over-calculation by the ECU. The air can also be recirculated back into the intake, a typical stock setup for cars with an upstream MAF sensor. The situation can also be corrected by switching the fuel metering system over to a manifold absolute pressure sensor, a conversion that usually requires a compatible aftermarket ECU or piggy-back fuel controller. The MAP sensor monitors the absolute pressure in the manifold at all times and will correctly detect the change that occurs when the valve vents, allowing the ECU to reduce fuel metering accordingly.

so according to wikipedia a BOV was developed as a work around to avoid compressor surge. compressur surge as we all know occurs when pressure past (after) the compressor wheel, exceeds pressure that the compressor cannot supply. that is, pressure exceeds far beyond what the compressor (and it's map) can actually supply. this is commonly observed with no BOV when the throttle body closes the built up pressure must go somewhere so it essentially collides mid air and causes the compressor wheel to surge. this human observation of this is the vl turbo tutututuutut noises. excessive surge on a compressor wheel can lead to failure.

this was debated about 1.5 years ago to death and i still couldnt see (and i still cant) any logical reason for installing a factory bov as an emmissions "fix".

i can however, see a logical reason why a factory bov is fitted, to avoid compressor surge

[R31 POWER]

Im with Mr. Untouchable. I removed the bov for 1 week for daily duties and it was a cop to drive. Between gear changes it felt like it took a little longer to boost up. Stock bov on and it's so smooth.

[squiggley]

+1 for stock bovs