Blowoff valve - wikipedia Blowoff valve A blowoff valve ( BOV ), dump valve or compressor bypass valve ( CBV ) is a pressure release system present in most turbocharged engines. Contents 1 Characteristics 2 Operation 3 Disadvantages 4 See also 5 References Characteristics A typical piston - type dump valve, used in auto racing. Unlike a blowoff valve, this one does not vent to the atmosphere. The small hose at the top is a feed from the intake manifold. A compressor bypass valve ( CBV ), also known as a pressure relief valve or diverter valve, is a manifold 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, ( sometimes `` hooter valve '' or BOV ) performs the same task but releases the air into the atmosphere instead of recirculating it. This type of valve is typically an aftermarket modification. 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. Blowoff valves are used to prevent compressor surge, a phenomenon that readily occurs when lifting off the throttle of an unvented, turbocharged engine. The sound produced is called turbo flutter ( the slang term ' choo - choo ' is sometimes used ). 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 resulting collision of pressure waves creates an effect similar to cavitation producing the unique noise. Operation When the throttle plate is open, the air pressure on both sides of the piston in the blow - off valve is equal and the spring keeps the piston down. When the throttle is closed, a vacuum forms in the manifold. This in combination with the pressurized air from the turbocharger moves the piston in the valve up, releasing the pressure into the inlet of the turbo ( Recirc. ) or the atmosphere ( BOV ). A blowoff valve is connected by a vacuum hose to the intake manifold after the throttle plate. When the throttle is closed, the relative manifold pressure drops below atmospheric pressure and the resulting pressure differential operates the blowoff valve 's piston. The excess pressure from the turbocharger is then vented into the atmosphere or recirculated into the intake upstream of the compressor inlet. Disadvantages In the case where a mass airflow sensor ( MAF ) is used and is located upstream from the blowoff valve, the engine control unit ( ECU ) will inject 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. An alternative method for utilizing both a MAF and a blowoff valve is to have the MAF located down stream between the intercooler and the throttle plate. This is known as Blow - through rather than the traditional Draw - through set up. Care must be taken as to the position of the MAF to prevent damage to the sensitive element. For example, on a SR20DET engine, the MAF must be at least 12 '' from the throttle plate, and the blowoff valve must be 6 '' from the MAF sensor. By using a blow - through method, the MAF wo n't be affected by the blowoff valve opening as the pressure is vented before the air reaches the MAF. One approach used to mitigate the problem has been 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. See also Wastegate Water hammer References Allard, Alan. Turbocharging and Supercharging. Cambridge, England : Patrick Stevens Limited, 1982. Gorla, Rama, and Khan, Aijaz. Turbomachinery Design and Theory. New York, New York : Marcel Dekker, 2003. Society of Automotive Engineers. Turbochargers and Turbocharged Engines. Warrendale, PA, 1979. Watson, N, and Janota, N. Turbocharging the Internal Combustion Engine. London, England : Macmillan Press Ltd, 1982. Automotive engine Part of the Automobile series Basic terminology Bore Compression ratio Crank Cylinder Dead centre Diesel engine Dry sump Engine balance Engine configuration Engine displacement Engine knocking Firing order Hydrolock Petrol engine Power band Redline Spark - ignition engine Stroke Stroke ratio Wet sump Main components Connecting rod Crankcase Crankpin Crankshaft Crossplane Cylinder bank Cylinder block Cylinder head ( crossflow, reverse - flow ) Flywheel Head gasket Hypereutectic piston Main bearing Piston Piston ring Starter ring gear Sump Valvetrain Cam Cam follower Camshaft Desmodromic valve Hydraulic tappet Multi-valve Overhead camshaft Overhead valve Pneumatic valve springs Poppet valve Pushrod Rocker arm Sleeve valve Tappet Timing belt Timing mark Valve float Variable valve timing Aspiration Air filter Blowoff valve Boost controller Butterfly valve Centrifugal - type supercharger Cold air intake Dump valve Electronic throttle control Forced induction Inlet manifold Intake Intercooler Manifold vacuum Naturally aspirated engine Ram - air intake Scroll - type supercharger Short ram air intake Supercharger Throttle Throttle body Turbocharger Twin - turbo Variable - geometry turbocharger Variable - length intake manifold Warm air intake Fuel system Carburetor Common rail Direct injection Fuel filter Fuel injection Fuel pump Fuel tank Gasoline direct injection Indirect injection Injection pump Lean - burn Stratified charge engine Turbo fuel stratified injection Unit injector Ignition Contact breaker Magneto Distributor Electrical ballast High tension leads Ignition coil Spark plug Wasted spark Electrics and engine management Air -- fuel ratio meter Alternator Automatic Performance Control Car battery ( lead -- acid battery ) Crankshaft position sensor Dynamo Drive by wire Electronic control unit Engine control unit Engine coolant temperature sensor Glow plug Idle air control actuator MAP sensor Mass flow sensor Oxygen sensor Starter motor Throttle position sensor Exhaust system Automobile emissions control Catalytic converter Diesel particulate filter Exhaust manifold Glasspack Muffler Engine cooling Air cooling Antifreeze ( ethylene glycol ) Core plug Electric fan Fan belt Radiator Thermostat Water cooling Viscous fan ( fan clutch ) Other components Balance shaft Block heater Combustion chamber Cylinder head porting Gasket Motor oil Oil filter Oil pump Oil sludge PCV valve Seal Synthetic oil Underdrive pulleys Portal Retrieved from `` https://en.wikipedia.org/w/index.php?title=Blowoff_valve&oldid=818758221 '' Categories : Engine valves Turbochargers Hidden categories : All articles with unsourced statements Articles with unsourced statements from April 2008 Talk Contents About Wikipedia Čeština Deutsch Français Italiano 日本 語 Norsk Norsk nynorsk Polski Русский Slovenčina Svenska Türkçe 中文 Edit links This page was last edited on 5 January 2018, at 11 : 52. About Wikipedia

Question: where does the blow off valve connected to
Answer: intake manifold after the throttle plate