BOV Question.

GizMo22t · Post by **GizMo22t** » Thu Apr 03, 2003 5:26 am

I have been pondering this question that a friend asked me. I couldn't give him a direct answer. The Question was....... What is the diffrence, if any, From a Blow off valve and a Bypass valve???? Please help

-K- · Post by **-K-** » Thu Apr 03, 2003 5:46 am

Well I have always used BOV to talk about a vent to atmosphere, Bypass to talk about a stock/bosch that pipes back in to the intake. BOV's generaly have some spring tensioner or valveing to keep them from leaking at idle.

vrg3 · Post by **vrg3** » Thu Apr 03, 2003 7:03 am

A lot of people call both types "blowoff valves." It seems like OEMs call them "bypass valves" while aftermarket manufacturers call them "blowoff valves." The distinction between the types is often made by saying "recirculating blowoff valve" or "atmospheric blowoff valve." They're also called dump valves.

GizMo22t · Post by **GizMo22t** » Fri Apr 04, 2003 6:36 am

Does a recurculating BOV mess with the mas air sensor? I noticed when I pulled the pipe off the Blow off valve and cap'd where it connects to the turbo, the car didn't run too good. Why is that?

vrg3 · Post by **vrg3** » Fri Apr 04, 2003 4:28 pm

No, a recirculating valve doesn't mess with the MAF sensor, since all the air that gets measured stays in the intake system until the engine consumes it.

When you pull the outlet pipe off the factory blowoff valve, you basically created a huge vacuum leak.

From what I understand, there are two ways for a blowoff valve to be actuated. Some types are actuated simply by a certain pressure; they act as check valves and allow the pressure to be relieved. Some other types (like ours) open when manifold vacuum is high. That means they open whenever the throttle plate is close to closed.

So, if that's true, when you pull the outlet pipe off you end up with the situation where at idle you have a nearly 1" wide hole in your intake piping. All this air comes in through the MAF sensor and goes right out through that hole.

GizMo22t · Post by **GizMo22t** » Sat Apr 05, 2003 1:59 am

Yea but I did cap the hole in the inlet. It felt like the car was running to rich on fuel.

vrg3 · Post by **vrg3** » Sat Apr 05, 2003 4:09 am

You capped all ends of everything?

GizMo22t · Post by **GizMo22t** » Sat Apr 05, 2003 9:28 pm

I capped the opening to the inlet form where the BOV used to blow into it. Pulled the pipe off the BOV and just left it to atmosphere.

vrg3 · Post by **vrg3** » Sat Apr 05, 2003 9:44 pm

So whenever manifold vacuum is high, that pipe is a huge vacuum leak because the valve is open.

...Right?

GizMo22t · Post by **GizMo22t** » Sat Apr 05, 2003 9:46 pm

On the BOV?

-K- · Post by **-K-** » Sun Apr 06, 2003 7:17 am

Yes, it is not made to run as a BOV. It will leak on idle. Reconnect it back to stock and if you need the sound get a BOV that is made for MAF cars.

GizMo22t · Post by **GizMo22t** » Mon Apr 07, 2003 3:11 am

thanks very much

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