General stuff, then ending with why to buy a PERRIN BOV or ALTA BOV
Why do you need a BOV? Every factory turbo charged car has a BOV. Turbo charged cars need BOV€™s to release the built up pressure from the turbo when the throttle is closed between shifts. With out a BOV, the pressurized air getting pushed backwards through the turbo stops the turbo from spinning. So a BOV is needed to keep the turbo spinning, which minimizes turbo lag between shifts.
So if a stock car has one, why do I need one? Factory BOV€™s are designed to hold factory boost levels. Some can€™t even handle them, that well. When the boost is turned up or a larger turbo is installed, factory BOV€™s will leak pressure causing loss in power. An upgraded Perrin BOV will solve the leaking issue and you will never have to worry about your BOV holding pressure ever again.
The more boost, the more pressure it holds regardless of spring rate!
No need to have a stiffer spring for high boost applications
Adjustable spring tension!
Adjustable flow rate!
BOV cap can be screwed in to increase tension on spring, to adjust how quickly the BOV vents.
Internal adjustment to adjust how much the BOV will flow while venting. It does this by changing the piston travel which allows the user to vent less air for lower boost applications, and more air for higher boost applications.
Will hold more boost, and flow more air than any other BOV!
Universal applications for tube to tube recirculation type BOV€™s (EVO, Eclipse, 1.8T€¦..)
Direct mount applications for WRX,
Vent to atmosphere applications for SRT-4, and other non MAF based systems.
With our Extensive testing on the WRX and EVO, we have found that 100% recirculating BOV€™s, always outperform vent to atmosphere BOV€™s. Since the VTA type BOV€™s don€™t vent the air back into the intake after the MAF sensor, the ECU will add fuel based on that amount of air it ingested, not the amount of air vented.
Since the intake/boost system on a MAF based car needs to be kept in a closed loop, venting air to the atmosphere causes the car to run very rich. This can cause drivability issues.
Get the sound of a VTA with a 100% recirculation BOV.
For cars that use a MAP sensor to determine fuel, don€™t matter.
BOV Directions PROTOTYPE VERSION
Remove the stock BOV
Install BOV at loosest settings to start with, please note the grooves on body
Leave the flow adjustment at factory setting.
Install the Black tube to the pressure source
Install the silver tube to the intake, or recirculate tube.
Install manifold vacuum source to the back nipple on the BOV.
BOV directions for the WRX
Remove the stock BOV
Remove the recirculation elbow from the stock BOV and using same bolts install onto the Perrin BOV and attaching the vacuum hose
Attach the flange to the BOV, and orientate the flange similar to stock. (Make sure to screw the set screws into the flange and tighten)
Install the BOV same as old BOV comes off, using same bolts
Rotating the flange may be necessary to get the recirculation hose in the right location.
Make sure the BOV clears the hood before closing.
BOV directions for VTA
Remove old BOV
Attach the black tube to the boost tube where factory BOV came from.
Make sure to orientate BOV so there is no interference with other parts.
Hook the manifold vacuum source to the top of the BOV
If tuning needs to be done to the BOV we have provided instructions how to do so. The cap should never be unscrewed past the o-ring, this will cause a boost leak and the BOV will not function correctly. The piston in the BOV should travel a minimum of 1/16€, please use this as a frame of reference when adjusting the BOV€™s spring tension. More spring tension is not needed to hold more boost. Adjusting spring tension is necessary to adjust how quickly the BOV closes and vents. The higher the tension, the slower the venting response.
1. Remove, or thread in completely the socket head screw to allow piston full travel.
2. Adjust the spring tension to desired venting response, or closing response. (Making sure to note what groove on the body, the cap is screwed down to)
3. With the car turned off, pull vacuum hose off the BOV and unscrew the socket head screw until it stops on the BOV cap.
4. Screw in 2.25 turns =1/16€ of piston travel
4.5 turns = 1/8€ of piston travel
6.75 turns = 3/16€ of piston travel
9 turns = 1/4€ of piston travel
11.25 turns = 5/16€ of piston travel
13.75turns = 3/8€ of piston travel
Stock setting is 3/8 from end of screw to nut, and cap screwed 13/16 from the top of the body.
The more the screw is turned in, the more air will vent from the BOV.
This part of the adjusting procedure can be done while the car is running for faster setup.
5. Once desired venting level is achieved, remove the BOV cap and spring
6. Carefully remove the piston and screw
7. Making sure to hold the threaded length of the screw tighten the nut down to the piston. This will hold the desired amount of piston travel.
8. Install the piston back into the body making sure to use a small amount of grease around the piston.
9. Install the spring and cap, and tighten cap down to mark as noted before on side of BOV.
[quote=nmwg;2473766][SIZE=2]This is a question about blow off valves more in general. I know what their basic functionality is: they release compressed air produced by the turbo when the engine no longer needs it. I know that they usually vent the air into the atmosphere. I have read that that can screw up the engine performance because it causes it to run rich. I am under the understanding that if you route the blow off valve output back to the intake before the turbo but after the mass airflow sensor, that fixes the problem, but the blow off valve doesn't make the sound that it is known for. If that is the case, does that mean that everyone who is running a loud blow off valve has poorer engine performance, or are there ways to achieve both?
The other question is: can someone explain how directing the blow off valve output back into the intake before the turbo and after the sensor fixes the engine running rich problem? My understanding is that the mass airflow sensor takes a measurement of the air coming in so that the computer can calculate the proper fuel air mixture for the given throttle position. If the throttle is in the closed position, that should mean that a minimal amount of air would be needed for the engine combustion, so the computer should only allow that minimal amount of air in for combustion. In the case of a system with a blow off valve, this scenario would cause the blow off valve to activate and release the extra air, thus creating a situation where there isn't a proper amount of air left for the computer calculate fuel amount. I can see how this makes the engine run rich for a moment. What I don't understand is how putting that air back into the system before the turbo helps the running rich problem. Reason being.... The mass airflow sensor is still calculating air coming in from the outside and is unaware of the extra air being put back into the system via the blow off valve. I would think this would create the situation where there is more air in the system than the mass airflow sensor calculated. Maybe that doesn't matter because the computer only takes what it needs for combustion, so that long as there is not a shortage, things run smoothly. This still leaves me with the question of: as long as the blow off valve is open, how does it matter to engine combustion whether or not the extra compressed air is vented into the atmosphere or back into the system since the blow off valve is redirecting all the air away from the engine. I would think that by the time that the recirculated air from the blow off valve got back to the point to be used by the engine at least one of the pistons would have fired rich, or that any needed air for a no throttle combustion could be sufficiently supplied from the standard air intake.
Thanks for your answers.
Blow off valves, recirc valves, dump valves, bypass valves pop-off valves and whatever you want to call them all do the same thing. They relieve boost pressure! In different car markets BOV€™s have different names which makes it a little confusing as to what they do. This makes all the BOV€™s confusing as to what they do. The easiest way to think of a BOV is a big valve. It just opens and closes relieving pressure at certain times.
First lets explain the basic turbo system. Under normal operating conditions (light load) the engine is sucking in air through the throttle body. The turbo sits upstream of the throttle body and is not doing much work at this point. As the throttle is opened more and the engine is under more load, the turbo starts to build boost. As boost goes up so do the power and the fun! When the throttle closes all that boost has to go somewhere, this is where the blow off valve comes into play! If the BOV doesn€™t exist, when the throttle closes the boost gets back up through the turbo. This back up of pressure puts great stresses on the turbo€™s compressor and turbine shaft and the air causes the turbo to slow down very quickly and abruptly. This phenomenon is called compressor surge. Compressor surge is not good for the turbo€™s longevity at all.
In the above situation, a BOV would be installed after the turbo, but before the throttle body. Under high load and light load the BOV would be closed (remember its valve). The BOV comes into play when the engine transitions from high load to light load. This is when the turbo is creating boost, then suddenly the throttle body is closed and the pressure needs to be relieved.
Seems simple enough, it gets rid of the pressure that builds up when the throttle closes abruptly like when shifting. How the BOV actually open and relieves the pressure varies slightly, but for the most part the BOV is actuated using 2 things, manifold vacuum and the boost pressure it is trying to relieve.
Under high load the boost is holding the valve close and as the throttle closes the vacuum now in the intake manifold starts to pull the valve open. On the opposite end of the valve the boost pressure still in the system also helps the valve open.
So now that you know how it works, lets add a few variables to what the BOV does with the relieved pressure. On all OEM applications the BOV vents the air back into the intake system. This is done to keep the noise down, and to keep unwanted emissions from getting into the atmosphere. The other option is to let the BOV vent the unwanted boost to the atmosphere.
There are 2 types of ECU€™s and how they make the engine run. One uses a MAF (Mass Air Flow) sensor which reads air flow, and the other uses a MAP (Manifold Absolute Pressure) sensor to calculate air flow. The MAF base systems have a sensor placed right after the air filter, where the MAP based systems have the sensor in the intake manifold.
Traditionally, a BOV, or blow off valve is one that blows the unwanted boost, out to the atmosphere
A recirc or bypass valve blows off the unwanted boost back into the intake system of the car.
How different BOV€™s effect how the engine works.
On a car that d
On the Mini the BOV is electronically actuated by the ECU.