BOV/BPV location on IC piping

[blacksheep]

Is there a general "best" location for BOV/BPV on IC piping:

Closer to TB on IC pipe
Closer to turbo on IC pipe
On the FMIC (Full-race does this)

Have always wondered about this

Lets discuss /ubbthreads/images/graemlins/smile.gif

 

[belize1334]

I put mine on the end-tank of my IC and now I'm getting compressor surge. I used to have the BOV mounted on the 2" pipe coming off of my j-pipe and it didn't surge then so it's gotta be the change in location that's done it. I think the problem is that the end-tank is such a large volume compared to the opening size of the BOV that the BOV "looks" smaller and doesn't vent as fast. I'm now on the verge of hogging out the hole to make it a little more "attractive" and possibly adding a second BOV on the other end-tank. For most people this would be prohibitive because of where the end-tanks are located on a FMIC but with my A2WIC I can get to both endtanks quite easily.

 

[prove_it]

It is best to have the BOV/Recirc valve as close to the throttle body as possble. This allows for the highest amount of "vent" and prevents compressor surge.

When you get into boost then suddenly close the throttle body the turbo is still spinning and creating boost. The air in the piping still has velocity and wants to travel forward. The throttle plate is closed and the air smashes against and reverses and heads back to the turbo. The closer the BOV is to the Throttle body the faster the air is purged and the less of a chance for compressor surge. If you have a ball bearing turbo its not as hard on the bearings to have surge, but either way it's not good.

Yes, it does matter where the BOV is located. Yes it can even kill a good turbo. Full races intercoolers are designed with ball bearing "big" turbos in mind.

 

[Barnes]

It doesn't quite work like that prove_it...

The air doesn't bounce back and 'hit' the turbo. It just stops. The throttle plate closes, the flow out of the turbo drops to zero, but the pressure is still high. So if you look at a compressor map of any turbo, and figure your running it in the middle of the map for instance, if you drop your flow to zero you can see you are now WAY left of the surge line. But even worse than a compressor stall, you now have a surge problem. All this pressure inside the piping wants to go somewhere. The only way, (without a BOV, or too small a BOV) is BACK through the turbo which is still trying to pump air into the IC piping due to the momentum of the compressor/shaft/turbine. This is where you can explode turbos. All that air running back through the turbo will be fighting against the compressor that wants to do that opposite. So you get bent blades, broken blades, or broken turbo shafts.

Point is this:
A) A BOV anywhere on the piping that is large enough will prevent compressor surge. A large enough BOV provides the path of least resistance for all that compressed air to escape.
B) A BOV's particular location on the piping probably has no distinct advantages. Theoretically putting it close to the throttle plate would keep a consistent flow direction. This would technically save energy as the air is always going the same direction and not reversing to go back out a BOV placed somewhere farther from the throttle plate. However the momentum of air is very low, so we are probably talking immeasurable amounts of power loss or loss of transient response.

The most important part is having a BOV that is large enough. Hell, get a couple blow off valves. More can only help. But location is not gonna make enough difference to care.

 

This has been discussed before and I'll say this again. I will quote myself: "It doesnt matter where you pop a balloon." Air is under pressure meaning it is pressing all side of the pipe and when discharged it escaped. It is not water sloshing around the you can vent it before it rolls back into the blades of the turbocharger. Critically think about the physics behind it and you'll realize it doesnt matter where you put it. Whereever the easist place to get it on there is.

Here is a thread of me being right in 2009:
2009
/ubbthreads/images/graemlins/smile.gif


Here is a thread of me being right in 2008:
2008
/ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/smile.gif

Barnes is right about volume. If you max out a 1g dsm bov and after it discharges you are still getting surge from it not moving enough air then 2 1g bovs would work. I have seen 600 hp cars on modded 1g bovs and not having issues moving enough air.

I have have cars with the valves on the hot pipe, cold pipe, on the endtanks and it just doesnt matter. If you are recirculating it then put it in the easiest path to vent back in.

 

[CarRacer]

I still remember your balloon popping analogy and is the easiest to visualize for me.

Whatever is easiest for mounting is best, and remember if you vent to atmosphere. Kill him in the face.

 

Quoting crankwalk:
This has been discussed before and I'll say this again. I will quote myself: "It doesnt matter where you pop a balloon." Air is under pressure meaning it is pressing all side of the pipe and when discharged it escaped. It is not water sloshing around the you can vent it before it rolls back into the blades of the turbocharger. Critically think about the physics behind it and you'll realize it doesnt matter where you put it. it then put it in the easiest path to vent back in.



You must have never taken any fluid dynamics classes then. Air is very much like water and air is much heavier then what many people think it is. Just imagine a river and the way it flows around a bend, it will create a low pressure area on the inside of the bend and pull much of the debree or pull a void and cause turbulence. This does the same thing in a pressurized pipe, on the short side of the bend you will have this same issue.

I agree that the BOV should be closer to the throttle body because thats were the air is being stopped and it starts to back up from that location.

 

[broxma]

Few things to work with here.

To the op, the flow rate of the BOV is more important than the location. It's ability to vent the air completely to achieve ambient pressure in the pipe is one of its functions. Having too small of a BOV can result in surge. I am not sure if the flip side of this, too large of a BOV has any ill consequences. No matter where you have the BOV, air will be colliding at it's exit from both directions. The flow through the core of an intercooler is large enough that a sudden release of pressure on one side of it makes no difference. In reality, regardless of which side you put the BOV, the intercooler experiences a large and quick decompression as does any volume of the piping from the compressor wheel to the throttle plate. In that respect, position is of no importance.

The INITIAL

 

I can tell that you and your wise old man have never worked with a wet flow bench before. Like I said, air is allot like water. Thats why the short turn in a cylinder head is just as important as the long side.

Im not here to argue, I gave my opinion and im stepping out. I know a bit about air flow though.

 

[JSchleim18]

^You ever get those flow bench numbers /ubbthreads/images/graemlins/hsugh.gif

 

[strokin4dr]

/ubbthreads/images/graemlins/rofl.gif You guys are relentless.

 

[Barnes]

Quoting BOOSTIN HARD:
Quoting crankwalk:
This has been discussed before and I'll say this again. I will quote myself: "It doesnt matter where you pop a balloon." Air is under pressure meaning it is pressing all side of the pipe and when discharged it escaped. It is not water sloshing around the you can vent it before it rolls back into the blades of the turbocharger. Critically think about the physics behind it and you'll realize it doesnt matter where you put it. it then put it in the easiest path to vent back in.



You must have never taken any fluid dynamics classes then. Air is very much like water and air is much heavier then what many people think it is. Just imagine a river and the way it flows around a bend, it will create a low pressure area on the inside of the bend and pull much of the debree or pull a void and cause turbulence. This does the same thing in a pressurized pipe, on the short side of the bend you will have this same issue.

I agree that the BOV should be closer to the throttle body because thats were the air is being stopped and it starts to back up from that location.



Wait.. what? Your river analogy has nothing to do with pressures and everything to do with fluid velocity. That's why debris gets deposited on the inside of the river bend, low velocity. Suspended particles settle out at lower velocities.

Even then, what is your point about flow around bends? You shouldn't put the BOV on the inside of bends? Regardless of any dynamic pressure differences across the flow inside the pipe, it will always have a much higher static pressure than the outside air. So regardless of where you put it, the air will flow out the BOV.

As for turbulence, the flow is probably already turbulent, but I'm too lazy to confirm that.

 

[prove_it]

This thread is very interesting. I know I got my flame suit on and I'm trying to learn from all of this.

By the way it does matter where you pop a balloon. If you poke it where the knot is it won't pop, it just leaks. Try it. Haha just throwing some crap at ya!

From everything I've ever read, it's a general precaution to mount the BOV as close to the T-body.

 

[Barnes]

Quoting broxma:
Any catastrophic bearing failure I have ever seen has been caused by either foreign object or improper oiling. I invite someone to find me a turbo with a critical failure due ONLY to surge. 18 years of doing this crap on my part has revealed not a single one. My old boss, who you all know or should know, has been at this game for 40 years and will tell you the same thing.




I have no idea who your boss is. However both Garrett and FP say turbos can fail due to surge. I for one will believe them.

Quote:
Airflow will compress on the long side of the pipe and speed up.



No. The air will not compress, it will do the opposite. Air along a streamline that increases in velocity will have lower dynamic pressure.

Quote:
The direct energy loss caused by directional change within a pipe can also be calculated. This is why I have long rallied against these intercooler designs with inlets and outlets which are at a direct 90 degree angle to the flow across the core. This is simply bad engineering.



Sure it can be calculated, but have you? I've long been opposed to sharp bends in end tank design, but there is one thing I have to consider. Does it matter? What actual pressure loss is induced by these bends? 1psi? 0.5psi? 0.001psi?? Perhaps you should take collect some empirical data and see if it really matters. As for engineering, well, true engineering is a balance. Time, money, performance, ease of install, etc etc. Making an IC with sharp bends generally (in GVR4 world) makes it much easier to install. That is a trade off, not bad engineering.

 

Quoting BOOSTIN HARD:


I agree that the BOV should be closer to the throttle body because thats were the air is being stopped and it starts to back up from that location.



Using that logic you would want it by the turbo so it all gets released as its going back towards the turbo. If all the pipes in the charge system are rushing back towards the turbo why would you want the vent right by the throttle body where the majority of the air is already PAST that point going back to the turbo? Yes, I know that air is like water in that it follows the path of least resistance but when it's under pressure it is not like a half empty bottle of soda being sloshed around, it's like a FULL bottle of soda that has been shaken up. When you poke a hole it escapes anywhere it can.

Since I haven't taken any fluid dynamics classes or work on cars for a living though it is almost impossible for me to understand how stuff works apparently. /ubbthreads/images/graemlins/dunno.gif




I'm going to stick with it doesn't matter where you put it. I have had plenty of success everywhere I have put them with the only factor that mattered was how much volume was being moved out after the TB closes and the next time I go WOT.

 

Crankwalk, you have to look at it like a column of mass. When that throttle plate closes, that air starts to back up making the column. When the column starts to get higher(backing up in the pipe) it creats allot of force on the throttle plate. Just take the throttle plate area and pie it to get your area. Now take that 25 psi inside your pipe and and figure out the amount of area in your pipe from your throttle plate to your BOV and that is the amount of force pushing onto the throttle plate. If you have the BOV closer to the throttle plate you will have a much smaller column of air that gets built up.

I really suck at explaning things on the net but PM me if you will like to talk over the phone. I can explain things much better that way. Not great but much better.

One thing I would like to say, God blessed me with some pretty good understanding on certain things and cursed me on others, like my super small penis, and my impotent problem and my pre-ejaculation situation, but he did give me the understanding of how air flows. /ubbthreads/images/graemlins/smile.gif

Now the cats out of the bag. /ubbthreads/images/graemlins/grin.gif

 

[prove_it]

I just reread broxma's post and yea it makes no sense to me.

So what are the ill effects of an over sized BOV? How would you know if you have too much?

 

[Barnes]

You can't have too big or too many BOVs. There is an optimum point of course. Sizing your BOV(s) just large enough so they aren't opening 100% is probably the ideal.

 

+1

 

[prove_it]

So given the physics and dynamics of the system, pressure moves high to low, blah blah blah are there any locations that could increase the flow rate through the valve? Basically making the purge quicker and more effient?