Science of a BOV placement

[absolute_DSM]

Ive been through WyoTechs High Performance Engine plus more and read multiple posts on where to place a BOV (near the TB or the IC)... but no posts really show which is better...

I see the a placement at the TB better so the air trapped when the plate closes doesnt have to turn around in the piping too far to get out... but then I see placing it closer to the turbo so when the plate closes, no more air gets pushed up towards the engine....

So whats "better" or is it all opinion? I dont care what looks cool, I want efficiency.

 

[HustlerTalon]

Just put it in the middle between the TB and the IC and don't worry about the science...on a more serious note though, the placement of the BOV won't affect the efficiency of your car. I mean if you are running 15psi for example, no matter where the bov is located, its going to escape immediately.

 

[fourreGsixty3]

Generalized companies place the flange for the BOV in the center of the UICP.I have never seen anyone place a BOV really close to the IC or TB.

Dustin

 

[slipstream808]

This is very anal retentive!! But that's OK, cause we are anal retentive guys.

Near the TB hands down.
1.) The air line to the BOV wont be as long so the BOV will open sooner
2.) The air will escape before it gets to the turbo. Helps the life of the turbo.

Who cares if more air gets pushed to the engine? It's not goin' in! And when you stomp on it, wouldn't all that "pushing" air be closer to the TB so it gets to the engine sooner?

Nuff said!

 

[Auto RS T]

It is my understanding that the function of the BOV is to relieve compressor surge.

So this may help with with the idea of the air pushing towards the engine, seems that you would want to keep the pressure away from the turbo and out the BOV.

As for placement, I'm not exactly sure what is better.

 

[kenamond]

Just put it in the middle between the TB and the IC and don't worry about the science...on a more serious note though, the placement of the BOV won't affect the efficiency of your car. I mean if you are running 15psi for example, no matter where the bov is located, its going to escape immediately.

I kind of agree that it doesn't really matter a whole lot if you're talking about a 1g BOV or any bolt-on device, but I've found that things that seem very simple at first can be much more complicated when you start delving into the details.

I think that the most important aspect of BOV design is how your turbo continues to spool. If you can keep the shaft RPM up during a shift, you get less lag in the next gear. I remember hearing Rod Millen's unlimited class Toyota rally car at Pike's Peak hillclimb in 1996, and you could hear the turbo SCREAMING every time he let off the gas. That car was a monster.

Anyway, I'm a scientist and love the science of all of the gizmos in our DSMs, so I hope this thread will get nice and techy .

 

[brute]

I don't think it matters either way. Put it where you want, as long as it's between the intercooler and throttle body. For what it's worth, WRX's have the BOV on one of the intercooler's endtanks.

You must be logged in to view this image or video.

 

[kenamond]

I don't think it matters either way. Put it where you want, as long as it's between the intercooler and throttle body. For what it's worth, WRX's have the BOV on one of the intercooler's endtanks.

You must be logged in to view this image or video.

Do you happen to know if it's on the inlet endtank?

 

[1stGenRocks]

that looks like its in the ic outlet where it goes to the throttle body

 

[kenamond]

that looks like its in the ic outlet where it goes to the throttle body

Seems like there are two competing factors w.r.t. BOV before vs. after the IC. If the BOV is before the IC, the compressor could recirc (or vent) with less restriction, but in that case, the pressure pulse from the closed throttle might be too much for the IC. If the BOV is after the IC, the IC doesn't see the pressure spike, but the compressor has to blow through the IC to recirc/vent. Don't know if the IC is that vulnerable to the pressure spike, but those end tank welds would see a pretty hefty load - and a Supra SMIC with its bent metal forks may pop...dunno.

Maybe two BOVs - one before and one after could be used. It'd be cool if the one before the IC could drop a fin into the flow to give a smoother exit path. But I always overthink everything

 

[dave99gst]

Closer to the turbo gets my vote -
I was going to mention that ive seen it mounted to the endtank of a fmic, but i see thats been covered.

 

[KScivic]

Damn good thread for the Newbie forum...

 

[MyBeatGSX]

Its been proven and I saw it explained in some book, as close to the TB as possible is the best location. This is for all the reasons that people previously mentioned. The only reasons to locate it on the IC end tank are fitment issues and bling/sound factor.

The BOV on the STi/WRX intercooler is about 2" from the TB. That IC end tank attaches directly to the TB.

 

[absolute_DSM]

Lots of nice ideas, thats what I like to see.

Itd be interesting to do a test to compare lag, turbo life, etc.

But it seems like the majority is for placement closer to the TB, and with great reasons.

 

[forcefed4]

I agree with close to the TB, I'll have to look for it , but I have seen an article on this somewhere...

It went something like " The purpose ot the blow off valve is to relieve the pressure pulses that happen when you close the throttle quickly. These pulses are what causes turbo surge (right word?) They start at the TB so you can catch them quicker if the bov is there"

 

[slipstream808]

I remember hearing Rod Millen's unlimited class Toyota rally car at Pike's Peak hillclimb in 1996, and you could hear the turbo SCREAMING every time he let off the gas.

Don't those cars have very advanced antilag systems so the turbo keeps spooling? I thought they did.

 

[kenamond]

Don't those cars have very advanced antilag systems so the turbo keeps spooling? I thought they did.

Considering that this is one of the only remaining unlimited class auto races, I wouldn't doubt it. Suzuki or Subaru (it's been 10 years) apparently ran a 2-engine setup in '95 or '94: one for the front wheels, one for the rear. My first impression when I first heard the car approaching the "flying W's" was that it didn't sound at all like a car - more like some space ship.

I still think that the anti-surge aspect of a BOV is only marginally important for performance, and how it helps keep the turbo spooled would be much more important. With that in mind, it seems that you'd want to recirc your exhaust through the turbine during a shift, too.

 

[Defiant]

First you have to determine whether it's a venting or recycling BOV. The DSM BOV is placed for recycling, and with the intent of keeping spool speeds up. The stock 2G intake even has a nozzle pointing toward the turbo for this purpose.
As for "efficiency", it won't much matter. Pressure in a closed vessel is equal everywhere in that vessel. Whether positive or negative.

 

[MyBeatGSX]

First you have to determine whether it's a venting or recycling BOV. The DSM BOV is placed for recycling, and with the intent of keeping spool speeds up. The stock 2G intake even has a nozzle pointing toward the turbo for this purpose.

I'd have to disagree with that. That nozzle is to prevent the BOV vent induced MAF spikes that are so common with metal intake pipes, its also for silencing the BOV. It has nothing to do with turbo spool.
Its also not a closed vessel. In this case you have the TB which was recently closed and the turbo which is still pumping air into the IC piping. This is why we have pressue waves in the intake pipe, the pressure is not equal, the air is flowing. Like a line of people running down a hall and through a door, they might all start off spaced the same distance (same pressure) but close the door and when they all start running into it you're going to get a build up of people (high pressure) at the door first. Put something in the way to stop the flow and the air piles up, higher pressure starts at the TB plate and travels backwards to the compressor that is still pumping air in. Same idea as attaching a slinky to a wall and boucing the waves back and forth if you ever did that one in middle school science class. The idea is to vent it as quickly as possible so it never gets anywhere near the turbo. Hence the placement as close to the TB as possible.


I'll also disagree with kenmond. You think the primary purpose is for turbo spool between shifts? Do you have any idea how severly damaged a turbo can get by running with no BOV? The pressure waves will kill the thrust bearing in short order and can even break a wheel or snap the shaft at high boost. Preventing this is the primary purpose of a BOV.

 

[housegsx]

I'd have to disagree with that. That nozzle is to prevent the BOV vent induced MAF spikes that are so common with metal intake pipes, its also for silencing the BOV. It has nothing to do with turbo spool.
Its also not a closed vessel. In this case you have the TB which was recently closed and the turbo which is still pumping air into the IC piping. This is why we have pressue waves in the intake pipe, the pressure is not equal, the air is flowing. Like a line of people running down a hall and through a door, they might all start off spaced the same distance (same pressure) but close the door and when they all start running into it you're going to get a build up of people (high pressure) at the door first. Put something in the way to stop the flow and the air piles up, higher pressure starts at the TB plate and travels backwards to the compressor that is still pumping air in. Same idea as attaching a slinky to a wall and boucing the waves back and forth if you ever did that one in middle school science class. The idea is to vent it as quickly as possible so it never gets anywhere near the turbo. Hence the placement as close to the TB as possible.


I'll also disagree with kenmond. You think the primary purpose is for turbo spool between shifts? Do you have any idea how severly damaged a turbo can get by running with no BOV? The pressure waves will kill the thrust bearing in short order and can even break a wheel or snap the shaft at high boost. Preventing this is the primary purpose of a BOV.

I don't really think the placement matters all that much, but this is the best explaination and answer so far.

 

[kenamond]

I'll also disagree with kenmond. You think the primary purpose is for turbo spool between shifts? Do you have any idea how severly damaged a turbo can get by running with no BOV? The pressure waves will kill the thrust bearing in short order and can even break a wheel or snap the shaft at high boost. Preventing this is the primary purpose of a BOV.

Come on now, give me a bit more credit than that! It's obvious that you don't want to surge your compressor. I said nowhere that you shouldn't have a BOV - that's rediculous. Aside from not killing your turbo , the performance considerations fall back to keeping whatever shaft RPM you have from dropping during a shift (and surge will drop them quite well), and it seems that the restrictive BOV valve, venting 90* out the side of a pipe, etc. is not going to do the best job at that, and having the turbo recirc through the IC which is a non-negligible restriction probably doesn't help either. And then you have the hotside which doesn't recirc at all.

Seems like a somewhat easy thing to do is vent before the IC (with GM MAS or whatever), but as I stated above, I don't know if the pressure pulse from the TB would damage the IC. And I kinda like my 2 BOV setup idea, too, which would spare the IC.

 

[Defiant]

I'd have to disagree with that. That nozzle is to prevent the BOV vent induced MAF spikes that are so common with metal intake pipes, its also for silencing the BOV.

I'll buy that.

It has nothing to do with turbo spool.

But not that.

Its also not a closed vessel. In this case you have the TB which was recently closed and the turbo which is still pumping air into the IC piping.

So, closed at the throttle plate, and being pumped into at the turbo side. Hardly an "open" vessel, hm?

This is why we have pressue waves in the intake pipe, the pressure is not equal, the air is flowing. Like a line of people running down a hall and through a door, they might all start off spaced the same distance (same pressure) but close the door and when they all start running into it you're going to get a build up of people (high pressure) at the door first. Put something in the way to stop the flow and the air piles up, higher pressure starts at the TB plate and travels backwards to the compressor that is still pumping air in. Same idea as attaching a slinky to a wall and boucing the waves back and forth if you ever did that one in middle school science class. The idea is to vent it as quickly as possible so it never gets anywhere near the turbo. Hence the placement as close to the TB as possible.

Or, tune it to find the place where the wave peaks, for optimal pressure release. The turbo won't care about those guys bumping (and, copping feels off the girls) down by the door, so long as they don't stack up to the blades. Are any setups used that have the BOV at the throttle?

I'll also disagree with kenmond. You think the primary purpose is for turbo spool between shifts? Do you have any idea how severly damaged a turbo can get by running with no BOV? The pressure waves will kill the thrust bearing in short order and can even break a wheel or snap the shaft at high boost. Preventing this is the primary purpose of a BOV.

At DSM levels of boost. My '84 Turbo 200SX had no BOV, only a pressure release for backfire. But it also only ran on the order of 4psi boost.