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Talk:Blowoff valve

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Who keeps erasing these pictures? Its not rocket science here people, I added a few arrows to the original pictures and made the text more clear. Whoever is

I am confused, Are blow off valves there for purely the sound? If they are supposed to improve engine performance, why don't the manufacturers add them to there vehicles? Even the Built for Performance Subaru WRX or STi don't add them. Should'nt the whoosh sound they make be going back into the engine for a good reason?

Atmospheric blowoff valves are primarily installed for sound. You will not find these on OEM vehicles because the majority of jurisdictions do not permit releasing compressed air or vapour from the engine to the atmosphere. This also explains why the PCV system also is routed to the intake.

Hackish (talk) 22:09, 5 March 2013 (UTC)Michael[reply]

They do have them, pretty much every turbo car since the late 80's has. —Preceding unsigned comment added by 71.98.246.103 (talk) 17:24, 14 September 2007 (UTC)[reply]

I'm don't really know much about this, but I hear they do have them but typically they will use a silenced version and stock cars are usually running a pretty low boost so it is harder/impossible to get much of a sound out of them. I don't think there is any difference in performance between muffled and unmuffled versions? Hullo exclamation mark (talk) 22:00, 3 October 2009 (UTC)[reply]

Pretty much every turbo charged car has a compressor bypass valve (i.e a 'blow off valve') but they aren't vented to atmosphere. This means you cannot hear it.

A dump/blow off/VTA/recic valve have the engineering value of maintaining the compressor flow above the surge line on the compressor map ---------

Maintaining the flow above the surge line prevents the compressor entering a stall/surge cycle which causes collapse of and re-establishement of flow in a rapid cycle. this will in the longer term damage the turbo. it DOES NOT reduce lag, it DOES NOT allow the turbo to keep spinning, infact by maintaining a flow which requires energy to move a mass, while there is no exhaust gas to expand across the turbine, the only energy available is the inertia within the spinning turbo. As such, it actually slows the compressor down quicker ! Some competion cars dont use such a valve and thus enter compressor surge. Its this noise you can hear in cars such as the 1985 Audi sport quattro.

Also, some motorsport regulations require a valve to vent excessive pressure to control boost and the power the engine develops, these are not the same. In some VERY high boost & flow applications, dump valves can have a roll in limiting the peak pressure effect of transient flow reversal. — Preceding unsigned comment added by 192.149.117.67 (talk) 01:38, 23 October 2018 (UTC)[reply]

Can blowwoff valve be installed on an automatic transmission? or do you have to have a manual transmission?  —Preceding unsigned comment added by 198.60.71.50 (talk) 16:02, 17 October 2007 (UTC)[reply] 

ANSWER: Blow Off Valves re there to limit compressor surge, which happens when boost is left in between the compressor side of the turbo, and the outside of the throttle body of the engine's intake, while vacuum is experienced inside the throttle body due to throttle being snapped shut from getting staight off the accelerator.

Both Manual and Auto's experience this, and in most modern turbocharged cars, both manual and auto's are fitted standard from the factory with plumb-back Blow Off Valves. —Preceding unsigned comment added by 122.105.122.17 (talk) 11:42, 24 March 2008 (UTC)[reply]

is it through that all cars should have blow off valves? —Preceding unsigned comment added by 190.59.61.60 (talk) 01:20, 14 March 2010 (UTC)[reply]

The article says "When the throttle is closed, the relative manifold pressure drops to below zero bar ..." I can understand how the relative pressure can drop below zero, but I don't think bar is measured on a relative scale. Would it be clearer if it were changed to "When the throttle is close, the pressure on the manifold side of the throttle drops below the pressure on the on [the other side] ..."  ? 206.9.215.123 (talk) 20:12, 20 May 2011 (UTC)[reply]

The article does not describe compressor surge correctly.

Stall/surge is a cyclic event when flow falls below the compressors surge line. Needs expanding to describe surge. Also when a bypass valve opens, the compressor will tend to slow quicker than one operating in surge. This can be explained by considering the energy used to maintain an air flow with the bypass open. As such, a bypass valve may increase lag slightly. — Preceding unsigned comment added by 86.159.244.116 (talk) 16:33, 31 January 2013 (UTC)[reply]

I have read that some modern turbo diesels have throttle plates either for emissions or performance reasons and also a BOV is advantageous over a stronger/better turbo (which can be costly and sometimes impractical) when employing high boost pressure in performance diesel applications.

Is there room to mention this here? — Preceding unsigned comment added by 188.65.97.65 (talk) 10:21, 13 June 2014 (UTC)[reply]

 — Preceding unsigned comment added by 192.149.117.67 (talk) 05:29, 1 September 2018 (UTC)[reply]