1g BOV question.

[Brent Hunter]

My 1g BOV blows air out of the release valve at idle, is this normal or does it need to be replaced?

[Jordan Kruger]

most bov's float at idle a little bit. When you are boosting it places enough pressure on the diaphragm to keep the valve closed. It could become more apparent when the spring becomes weak after years of wear.  Do a boost leak test, and spray windex or a real leak detector on it. If it holds boost shes good. If the valve almost floats at idle it will definitely react quick to on and off throttle conditions.  I set my Greddy type R close to that, then tightened it up a tad. Works great. With that being said, you also want to be sure that the valve isnt floating to the point where you are wasting boost. Or pre-boost vacuum. If the valve stays open when you are trying to get into boost, then you will lag a bit for sure.

[Matt Vangaalen]

From what I've read a 1G BOV should hold 21psi. Your not makin boost at idle your valve might be stuck open. Do a boost leak test to see when the valve opens.

[John Hartman]

most won't hold 21.  Just the few, the rare, the one sitting in a box in my garage.

Most will start to leak a wee bit at 16 or so.  Some are good to 19ish.

Now, that said, boost pressure ability has nothing to do with leaking at idle.

And, if you are running it with the recirculate hose off, with a stock computer and a mass airflow meter in place, you need to put the hose back on.  If it leaks at idle, it does not matter at all if the air is going back into the intake pipe


The air that was counted by your mass airflow sensor is lost when you shift, or sit at idle.  Your car will run way to rich(not when on boost, only at idle and on shifts).  This will cause poor mileage, you WILL fail aircare, you will carbon up your combustion chambers and get hella knock thats really hard to get rid of, and a few other things. 

If you MUST vent your bov, just for the sound, then you need to run a speed density setup.

[CamWeiss]

Don't crushed 1g bov's hold a little more than 20?

[John Hartman]

can definately do, yes.  and the mod that adds a second vacuum line will definately hold more, up to 30 or more.

the crushed ones can cause other issues tho.

[Brent Hunter]

I'm running a 3" GM MAF ans V2.0 MAF translator. And yes I'm venting.

[John Hartman]

ahh, with that setup you can vent if the MAF is after the bov(IE in the upper intercooler pipe closer to the throttle body)

And if so, a leak at idle doesnt matter at all

[Matt Vangaalen]

Brent how is that maf translator workin for you? I have one sittin in a box waiting to buy afpr so I can put my fuel upgrades in