Venting the BOV on a fd3
 

hi guys,

I have a stock fd3 and have vented the BoV to the atmosphere. Have I done so correctly and are there no negative consequences?

Thanks

Hein (South Africa)

It is fine on a FD to vent the BOV to the atmosphere. FD's are speed density tuned, therefore they have no MAF-So you are good. The only major problem with BOV venting to the aptmosphere is on vehicles with an MAF, when you are running boost and then punch in the clutch it can stall the engine or cause it to run rich. Since the BOV is located between the TB and the MAF(on cars like the supra for example), the ECU thinks it got a lot more air than it actually did(when the BOV opens) causing it to run rich or not open the IAC letting it stall.

HTH,
Kevin

Thanks Kevin. I do like the sound!

Is this an acceptable way to vent the BOV to atmosphere? I like how easy it temporary it is executed!

typically on the venting side of the bov you dont need to put any type of filter/screen/rag. when that side of the bov is opened there is always air headed away from the valve so it cant enter the system

Thanks guys. Very useful. Can't wait to make her go a little faster. Look forward to helpful tips on that front too!

best of luck

Not necessarily so. The spring on the stock BOV isn't very strong. At idle if you listen closely you can hear it sucking air. It's not much but it's unfiltered.

agreed that putting a rag/"filter" on it is a good idea

The stock BOV is a diaphragm style, so it doesn't maintain a constant gate pressure like most aftermarket units. Most factory turbos are outfitted with these because they are quieter and more marketable to the general public. As you accelerate the extra boost pressure closes the valve and allows boost to build without a leak.

However when cruising and at idle the fd is in vacuum, so the stock BOV is venting to the atmosphere. So hot post-turbo air is being vented directly into your engine bay. I know this from personal experience. I love the sound most BOVs make so I vented mine. I didn't use a filter. I just plugged the hole in the air box and left the BOV hanging there. A quick drive up the highway shot my water temps into the 240s because the hot air was being vented right out onto the radiator. I reconnected the BOV and the problem was solved.

You'll notice the stock air box has a side vent with a tube that helps guide the hot blow-back air out and away from the engine.

how is the BOV venting if the car is in vacuum?

:scratch: And that is a vent tube, but pretty sure it's to vent positive pressure from the BOV.

The "gate" on the stock bov flutters like a throttle body plate not like a piston. So unless there is enough pressure on the valve to keep it closed, air is free to flow in or out. So unless you are boosting, the valve is slightly open. The weak spring on the stock bov is a result of its design. After market units have stiffer springs that keep the gate closed unless there is sufficient back pressure to blow it open. The stock bov only fully closes in the presence of boost. So during weak acceleration the bov vents some air out. It is a designed boost leak to help minimize noise. If the stock valve stayed closed like an after market unit it would be more audible during slower acceleration, resulting in a louder whoosh sound. During hard acceleration the valve is closed fully by the excessive boost and pressure builds. The loudness of the car overpowers the bov whoosh being recirculated. Manufacturers do this because the general consumer doesn't want their car to be noisy.

Vaccuum is the engine sucking in air to maintain its cumbustion cycle. When you accelerate the boost generated is then excess air being forced into the engine. So during "vacuum" air will travel through the intake tract through the easiest path. On some FDs the valve on the BOV is weak or loose and air is sucked in through the bov at idle/vacuum because it is the easiest path. On some the path of least resistance is through the turbos, the usual path. As air is pulled through the y-pipe, some is pushed out the bov. It is called a pressure head. The force in the system pulling air to the throttle body results in positive energy that creates an outward flow of air through the bov.

I hope this explains it a bit more.

I have to correct myself. CT9AIX was correct. The valve is weak on the stock BOV and at idle you can hear it venting a little. If vacuum is raised slightly it will then close completely and of course, when the throttle-plates close it will vent boost. It is unfiltered but it's unfiltered vented air (going out of the BOV) and tends to leave a little oil over time on whatever it's lying next to.
Only out while the engine is running. Not sure about the rest of your post.

Speaking in terms of aftermarket BOV's, if it is sucking air at idle or doing anything other than venting air when there is vacuum in the intake manifold and boost in your intake piping(ie anywhere before TB) it needs to be adjusted. Adjusting instructions can be found on several websites, turbosmartusa has some of the best. BOV's are about preserving the life of your turbo by preventing flutter. An improperly adjusted BOV can cause damage to your engine by letting unfiltered air in or damage incurred by vacuum leaks. I don't care much for BOV's and i have not really seen much benefit in terms of turbo life as far as street use goes, but some disagree. There is no performance benefit from them.