by-pass vs BOV?

What is the diffenence and is one better than the other?

 

A BPV (bypass valve) vents the excess pressure from a turbo setup back into the intake runners. A blow off valve vents the excess out into the atmosphere (engine bay).

 

Oh, and as to which one is better. It really just depends on your setup. My daily is an Impreza WRX, and i run a BPV on it. I've heard stories about BOV causing the engine to run a little too rich, but i'm not sure if that only applies to ECU controlled engines. A BOV would be easier to run on a custom turbo setup for a buick since it would involve less plumbing. The blow off valves do make that cool "woosh" sound if thats what you're after.

 

Lets see, 462, 3 inch exhaust, 413 cam with Procharger. Who's going to hear a little "woosh" :laugh:

Another question, does the BOV limit boost? As far as I can tell the Bosch BPV only responds to vacuum.

 

I don't think that BOV's are designed to limit boost, but i could be wrong about that. At a certain point a BOV valve will leak pressure to the atmosphere (depending on brand/model/etc) regardless. A wastegate/boost controller would limit boost if that's what you're after. As far as I know though, BOVs are to allow the pressure of a turbo system a place to escape during shifts/changes in RPM when the throttle plate is closed. I think their main purpose is to prevent compressor surge in the turbo.

 

Yes, and high boost systems should run A BOV to prevent damage from pressure spikes when the turbos are spinning fast, but the throttle is suddenly released. I'm adding a 2nd BOV to the Skylark for faster evacuation. With just the one (not very big) the boost still stacks up faster than the turbos slow down, and you can hear the boost making its way out the compressors in a back and forth fashion after the initial BOV gust.

BOV's are adjustable for how much force they will hold. If they are set too loose they will leak, but probably not enough to limit boost much. If set too tight, they don't open as easily, and limit the pressure relief. If I set mine too loose, it makes a buzzing sound as boost comes on from it bouncing open and shut slightly. I like to set it just a bit more snug than needed to eliminate the buzzing. That way it holds the boost with no leaks, but is very quick to respond.

The noise from the BOV is much louder than anything else going on at the time it opens.

 

BPV this is what all stock vehicles use and it opens with vaccum applied no matter what.
You will need to run a filter of some sort on the outlet of this type so it doesn't suck in crap under part throttle conditions.

BOV is only an aftermarket part and needs both vaccum source and boost to open. This means you won't need to run a filter of any type on it, because it will never be open under vaccum conditions. (idle/cruise)

I would suggest the biggest BOV you can get, it will move the most volume of air the quickest, also I would suggest installing it before the intercooler due to your car being an automatic.

Hope this clears it up alittle for you. And don't be concerned with any AF driveablity issues while running either valve, the condition mentioned by another memeber of rick issues is only on MAF cars with a BOV, because of the unmetered air issue.

 

Good to know. I thought the rich condition had something to do with the ECU expecting a certain amount of air to be in the system still.

 

Logan you are correct, just didn't seem to any clear answers posted so I put all the explanations into one post. The deal with your Subie is that the BOV being after the MAF sensor the engine gets less air then expected so you will get rich upshift issues, unless you tune the computer for this.

 

Thanks for all the answers. Right now I am running a butterfly style by-pass valve. At this point I am venting to the atmosphere. With a supercharger you do not have to worry about anything getting sucked into the outlet becuase you always have positive pressure. Eventually will plumb it back into the inlet side of the system.

The butterfly style does not make any real noise. Seems to work fine so far with the amount of boost I am running.