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      06-12-2009, 01:20 AM   #2
Terrance28
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My bov stays open also on idle but it doesn't suck air in rather blow out. Here just read this it will explain alot on how a bov works. Springs don't close the bov high vaccum and boost does.

The Blow Off Valve (BOV) is one of the most misunderstood products in the automotive aftermarket. The goal of this article is to clear up some of the common myths about BOVs and explain how blow off valves really work and how to adjust them properly. Please read this article in its entirety prior to installation of any aftermarket BOV; your turbochargers life may depend on it!

As you know, the purpose of a BOV is to make that cool "PSSSSHHHH" sound when you let off the accelerator. The secondary purpose is to prevent waves of high pressure from slamming into the compressor wheel on your turbo when your throttle plate slams shut, extending turbo longevity.

BOV Myth #1: The adjustment screw on top of an aftermarket BOV adjusts the sound that the BOV makes.

This is the most dangerous myth of all. If you hear a different sound from adjusting this screw, it means you are getting compressor surge which could destroy your turbo.


All this screw does is adjust the preload on your BOV spring. BOV's have a small metal plate on top of the spring. The screw screws directly into this plate, compressing the spring. Tightening it (turning it right/in) will compress the spring, increasing the spring energy. Loosening it (turning it left/out) will decompress the spring, lowering the spring energy. (Side note: you can achieve the exact same effect by placing washers/shims on top of the BOV spring.) As you will read below, the BOV spring should be adjusted to the lightest level possible while still holding your BOV shut during high vacuum conditions.

BOV Myth #2: The spring in a BOV holds the BOV closed during moments of high boost.


First thing is first: The purpose of the spring in a BOV IS NOT to hold your BOV closed under boost pressure! Selecting a spring based on PSI is incredibly confusing/meaningless and it makes us wonder if the people who pioneered aftermarket BOV design in the first place even understood how they work.

All BOVs have a reference line coming into the top of the BOV from your post-throttle body intake manifold. Under high boost, the force holding the BOV closed is BOOST! The pressure coming through the reference line is equal to the pressure under the BOV piston. Therefore a VERY mild spring will hold it shut just fine under these conditions.
Rather, the purpose of the spring in a BOV is to hold the BOV closed when your throttle plate is closed, IE during idle and deceleration conditions. Under these conditions, the vacuum in your intake manifold is much higher than the vacuum in your intake piping (therefore under the BOV piston) so the BOV has a natural tendency to spring open. Being open isn't even a problem if you are recirculating your BOV into your intake, however if you are NOT recirculating, it can allow unfiltered air into your intake which IS a problem.

Therefore, your goal when selecting a BOV spring and adjusting the BOV should NOT be to select a spring based on your boost level; that makes no sense. Your goal is to get the BOV to stay CLOSED during high intake manifold vacuum/closed throttle plate conditions, using the very smallest amount of spring energy possible. Using less spring energy will allow the BOV to snap open as rapidly as possible when pressure release is necessary


Have a friend just touch or push the gas pedal and you look at the bov piston it will shut, now if you are under boost or high vaccum it will stay shut.
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