{"id":2852,"date":"2019-05-22T18:05:48","date_gmt":"2019-05-22T22:05:48","guid":{"rendered":"http:\/\/maxtorqueperformance.com\/?p=2852"},"modified":"2019-05-22T18:13:51","modified_gmt":"2019-05-22T22:13:51","slug":"do-you-really-know-what-a-blow-off-valve-does","status":"publish","type":"post","link":"https:\/\/maxtorqueperformance.com\/staging\/index.php\/2019\/05\/22\/do-you-really-know-what-a-blow-off-valve-does\/","title":{"rendered":"Do You Really Know What A Blow-Off Valve Does?"},"content":{"rendered":"
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By Greg Acosta<\/a>\u00a0<\/span><\/span><\/span><\/div>\n


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When it comes to forced induction, even the most peripheral turbocharger enthusiast is familiar with the component in the system known as a blow-off valve (often abbreviated \u201cBOV\u201d). While that may be due in large part to the fact that it is responsible for the trademark \u201cwoosh\u201d noise associated with turbochargers, it serves a very critical purpose in a properly engineered turbocharger system.<\/p>\n

However, as Ben Strader of EFI University has found in the course of his various performance classes, the blow-off valve\u2019s true purpose is often misunderstood, even by the most knowledgeable enthusiasts. So even if you think you know what it\u2019s for, read on, and we\u2019re willing to bet you learn something new.<\/p>\n

\u201cMost people are familiar with the wastegate, and that its job is to control the amount of boost that is produced,\u201d Strader says. \u201cBut a lot of people have misconceptions about what the blow-off valve actually does.\u201d In the above video, he aims to clear up those misconceptions.<\/p>\n

The Basic Problem<\/strong><\/h4>\n

In order to understand what a blow-off valve is doing, you have to understand the inherent problem that exists in a turbocharged engine. \u201cWhat will happen is when you are driving along at wide-open throttle in full boost, and you quickly close the throttle, all of the air that was coming out of the turbocharger gets stopped by the throttle plate. That air has to go somewhere<\/em>,\u201d explains Strader.<\/p>\n

Without any kind of pressure relief, like some OEMs have done in the past, that air needs to go somewhere, and that usually means it comes back out of the turbocharger. \u201cWhat happens is that air gets stacked up [in the charge pipe] and wants to reverse into the turbocharger. That causes a situation called \u2018compressor surge\u2019,\u201d says Strader. \u201cSurge is a condition where the blades of the turbocharger can no longer create pressure coming out of the turbo. That causes them to slip, or \u2018surge\u2019.\u201d<\/p>\n

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To alleviate that problem, a pressure relief valve is placed in the system. There are several different types of valves, used for different reasons, but for the sake of this article, we\u2019re going to stick with straight vent-to-atmosphere blow-off valves. \u201cWe can put this blow-off valve between the throttle and turbocharger. That way, when the throttle closes, the manifold sees vacuum, that in turn opens the valve, and lets the air that is otherwise trapped between the turbocharger and closed throttle plate \u2018blow off\u2019. Pretty simple,\u201d says Strader.<\/p>\n

What\u2019s There To Understand, Then?<\/strong><\/h4>\n

It seems simple, the blow-off valve relieves the pressure in the system, when there shouldn\u2019t be any. Boom; end-of-article, right? Well, not really. This is EngineLabs and we like to dive a lot deeper into things than that, as does Strader, which is why we kinda like him.<\/p>\n

\u201cWhen I ask people: \u2018Why do you want to prevent compressor surge?\u2019 the most common answer I get is usually some form of, \u2018So that the backup of air doesn\u2019t slow the turbocharger down,\u2019\u201d says Strader of his experience in his classes. That answer, which is commonly held among the turbocharger community, is actually the opposite of correct.<\/p>\n

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