venting bov into maf intake stream?

[codyhoover]

go ahead and tell me i'm wrong but.....<P>filter->turbo->intercooler->bov->mas->tb<BR> <BR>you could still dump to atm because the air hasnt been measured yet. and as far as i know you can use mas under boost its the vaf that doesn't work. although our ecm(v6) need the signal from a vaf(volumetric flow rate) not a hotline mas(mass flow rate) so your looking at stand alone or some wierd piggy back ****.<p>[ November 25, 2002: Message edited by: codyhoover ]

[rikymaru]

Cody:<P>I understand how you could think that. But you left out the most important part. AFTER the filter is the MAS (Mass Airflow Sensor) <P>Not that I want to sound patronizing but that reads quite well for itself. It is a Sensor that measures the incoming Mass Airflow. RIGHT after the filter your car has guessed how much air will be coming into it. By venting to the atmosphere you lose the air that has been counted. Simple as that.

[dreamsforgotten]

I'm not that well aquainted with forced induction and I plan on getting the BPT swap in 2-3 months on my RS. So far this message board has given me all I need to start off. My only question (Excuse my ignorence) but with the blow of valve being used to release pressure that builds up and causes to turbo to try to spend the other way thus shortening turbo life, won't routing the air right back into the system defeat the purpose of a bov? Sorry I'm just not understanding.

[rikymaru]

"I'm not that well aquainted with forced induction and I plan on getting the BPT swap in 2-3 months on my RS. So far this message board has given me all I need to start off. My only question (Excuse my ignorence) but with the blow of valve being used to release pressure that builds up and causes to turbo to try to spend the other way thus shortening turbo life, won't routing the air right back into the system defeat the purpose of a bov? Sorry I'm just not understanding."<P>lol. You sound like me a good 8 months ago. I know it doesn't make any sense but look inside a CBV car. The whole reason you have excess air is due to the turbo. When you shift at 1-3k RPM's you really aren't boosting that hard. So the excess air from the turbo won't harm the throttle plate (unlike, say, 6k RPMs) So what do we do to save the throttle plate? We take the air BEFORE it can hit the throttle plate and throw it back into the intake so we can have more air available. Basically, the air will be made "usable" again. Just think of it as recycling air. Go to <A HREF="http://www.vfaqs.com" TARGET=_blank>www.vfaqs.com</A> and click on the intake or the turbo section. This will give you a perfect visual of what a MAF-equiped car looks like.

[pelado]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by rikymaru:<BR><STRONG>"I'm not that well aquainted with forced induction and I plan on getting the BPT swap in 2-3 months on my RS. So far this message board has given me all I need to start off. My only question (Excuse my ignorence) but with the blow of valve being used to release pressure that builds up and causes to turbo to try to spend the other way thus shortening turbo life, won't routing the air right back into the system defeat the purpose of a bov? Sorry I'm just not understanding."<P>lol. You sound like me a good 8 months ago. I know it doesn't make any sense but look inside a CBV car. The whole reason you have excess air is due to the turbo. When you shift at 1-3k RPM's you really aren't boosting that hard. So the excess air from the turbo won't harm the throttle plate (unlike, say, 6k RPMs) So what do we do to save the throttle plate? We take the air BEFORE it can hit the throttle plate and throw it back into the intake so we can have more air available. Basically, the air will be made "usable" again. Just think of it as recycling air. Go to <A HREF="http://www.vfaqs.com" TARGET=_blank>www.vfaqs.com</A> and click on the intake or the turbo section. This will give you a perfect visual of what a MAF-equiped car looks like.</STRONG><HR></BLOCKQUOTE><P>That's one of the worst explanations I've read in a long time. Here's my conception of BOV and this thread's topic:<P>The Blow-Off Valve is there to relieve the pressure downstream of the Turbo but upstream of the TB plate that closes when you shift. The pressure must be relieved since this high backpressure will essentially choke the turbo and cause its speed to drop. This has NOTHING to do with protecting the throttle plate. It has EVERYTHING to do with keeping the Turbo spinning up.<P>Routing the BOV discharge back to the suction of the turbo is taking the hight turbo discharge pressure to an area of<BR>low pressure, namely, the suction of the turbo. Routing the discharge between the MAF/VAF and Turbo suction prevents an overly rich condition that would be present if the air were simply exhausted under the hood.

[OsoSlo z28]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by pelado:<BR><STRONG><BR>The Blow-Off Valve is there to relieve the pressure downstream of the Turbo but upstream of the TB plate that closes when you shift. The pressure must be relieved since this high backpressure will essentially choke the turbo and cause its speed to drop. This has NOTHING to do with protecting the throttle plate. It has EVERYTHING to do with keeping the Turbo spinning up.<P>Routing the BOV discharge back to the suction of the turbo is taking the hight turbo discharge pressure to an area of<BR>low pressure, namely, the suction of the turbo. Routing the discharge between the MAF/VAF and Turbo suction prevents an overly rich condition that would be present if the air were simply exhausted under the hood.</STRONG><HR></BLOCKQUOTE><P>bingo

[92RedMX3]

Ok, dont laugh at me but now I am somewhat confused. I knew what the BOV was for but the routing it back to between the MAF & the turbo suction is new to me. Does this add enough pressure to the turbo inlet to make it appear to the MAF that there is not as much air coming in so that it will lean it out some?

[pelado]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by 92RedMX3:<BR><STRONG>Ok, dont laugh at me but now I am somewhat confused. I knew what the BOV was for but the routing it back to between the MAF & the turbo suction is new to me. Does this add enough pressure to the turbo inlet to make it appear to the MAF that there is not as much air coming in so that it will lean it out some?</STRONG><HR></BLOCKQUOTE><P>No. It just means that this air the BOV is sending back to the suction of the turbo was already measured by the MAF/VAF. The ECM uses this air signal along with a few other things to determine the amount of time the fuel injectors are open. <P>Now you take some of the air the MAF/VAF has already measured, blow it out the side of the intake during a shift and you get an overly rich mixture. When you complete the shift a lot of black smoke comes up. <P>Route the air back to the suction of the turbo (but downstream of the MAF/VAF so it doesn't read this as even more air coming in) and this air is recirculated quickly back through the turbo in the time it takes to complete the shift and you don't get the black smoke out the exhaust. <P>Besides the smoke, too much fuel drops the cylinder temperatures so much that less cylinder pressure is developed and less power is made. OK?

[92RedMX3]

ok, so it is the fact that the pressure in the line drops too much that that when the TB opens it doesn't have enough pressure to push enough air in to get that perfect 14:1 that it wants.? I hate to sound so stupid and I do understand how much of this works but this just baffles me for some reason but I am trying to learn.

[Ryencool]

ill try to expalin simply.<P>Your car meters the amount of air going in, when you shift the air sits still in front of the throttle body, when you open the throttle the throttle body opens and the air measured by your car mixs with the fuel.<P>However if you let off the gas, then the air measured by your car , sitting next to the throttle body, changes. It leaves the throttle body into the engine bay via a BOV. However it was laready measured by your car, and when you hit the gas, that air wont be there when the throttle body opens, and your car thinks it will, therefor you get the fuel mixture for air you dont have, get it?<P>however venting back int othe inatke that air is constantly there and does not leave the cycle..

[rikymaru]

"Routing the BOV discharge back to the suction of the turbo is taking the hight turbo discharge pressure to an area of<BR>low pressure, namely, the suction of the turbo. Routing the discharge between the MAF/VAF and Turbo suction prevents an overly rich condition that would be present if the air were simply exhausted under the hood"<P>You basically said in more technical terms the exact same thing I said. Up until this point. See, I have to ask: How do you vent safely? According to the above explanation you can't. And we all know people do it safely :-/ The turbo does work like a vacuum but a low pressure charge in the back of the intake makes no difference in damage. Yes, a CBV balances it out but if you are pulling the excess amount of air and there is NO way to balance a perfect vacuum throughout the ENTIRE intake system.<P>Another thing that got me: "This has NOTHING to do with protecting the throttle plate. It has EVERYTHING to do with keeping the Turbo spinning up."<P>Fine. ****ing shoot me. That was just my mind mixing up two thoughts at once. I have said REPEATEDLY THROUGHOUT THE TOPIC that the point of the BOV is to save your turbo. But to go back into the turbo it has to....CRASH INTO THE THROTTLE PLATE. :rollseyes: Yes, the turbo will go before the TP but it still will take abuse. Oh, and onother thing: some turbo cars (the 280ZX Datsun turbos come to mind) didn't come with a blow off valve. Thats why I said its there for spool up past, say, 5 psi.<P>*ahem* <BR>The purpose of a blow off valve or compressor bypass valve is to prevent large pressure spikes in the intake pipes when the throttle plate is closed while boosting, preventing the turbo from surging. The BOV sits between the turbo and the throttle body and has a vacuum line that is attached to both the other side of the BOV valve and the intake manifold. When you are boosting the pressure on both sides of the valve is essentially equal because the pressure in the intake manifold is the same as in the intake pipes. When you close the throttle plate while boosting all that air slams into the plate and pressure spikes. At the same time the intake manifold pressure drops to a vacuum, and thus so does the pressure on the other side of the valve. The result is the valve opens wide to allow the pressure to vent out. Also included in a good BOV is some form of spring to aid in keeping the valve closed during modulating part throttle situations so that the BOV doesn't open and cause drivability problems. <P>Thats textbook. Check it against everything I've been saying.

[pelado]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by rikymaru:<BR><STRONG><BR>The turbo does work like a vacuum but a low pressure charge in the back of the intake makes no difference in damage. Yes, a CBV balances it out but if you are pulling the excess amount of air and there is NO way to balance a perfect vacuum throughout the ENTIRE intake system.</STRONG><HR></BLOCKQUOTE><P>I just don't know what to say about this. <P> <BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by rikymaru:<BR><STRONG> Fine. ****ing shoot me. <P>I have said REPEATEDLY THROUGHOUT THE TOPIC that the point of the BOV is to save your turbo. But to go back into the turbo it has to....CRASH INTO THE THROTTLE PLATE. :rollseyes: Yes, the turbo will go before the TP but it still will take abuse. <P>Thats textbook. Check it against everything I've been saying. </STRONG><HR></BLOCKQUOTE><P>You didn't copy enough "textbook".<P>You're still wrong. The BOV isn't protecting the turbo. A turbo won't be damaged by the throttle plate going closed. Maybe I'm wrong but I thought the BOV's purpose is to keep the turbo spinning at a high rate so that boost pressure isn't lost when the throttle plate closes during shifting. But WTF do I know? [img]shrug.gif"%20border="0[/img]

[maldo]

You are right and wrong. The closing of the throttle plate doesn't damage the turbo per say. The BOV is there to protect the turbo and yes it is there to ensure the turbo keeps spinning in the right direction. The closing of the throttle plate forces all the "boosted" air to bounce off the plate and head in the opposite direction. Without a BOV, the air slams into the turbine, slowing down the spin and in some cases it can reverse the direction. If this happens, the damage can be quite extensive. Once pressure is built up with the plate closed, the BOV pops open, relieving the excess pressure, protecting the turbo from possible damage.

[rikymaru]

"You are right and wrong. The closing of the throttle plate doesn't damage the turbo per say. The BOV is there to protect the turbo and yes it is there to ensure the turbo keeps spinning in the right direction. The closing of the throttle plate forces all the "boosted" air to bounce off the plate and head in the opposite direction. Without a BOV, the air slams into the turbine, slowing down the spin and in some cases it can reverse the direction. If this happens, the damage can be quite extensive. Once pressure is built up with the plate closed, the BOV pops open, relieving the excess pressure, protecting the turbo from possible damage."<P>Thank you. That is what I have been saying. It's just simple physics: If we are running, say, 18 psi of air into the engine and we suddenly CLOSE the throttle plate then where does the air go? It can't go forward into the throttle body. Therefore it must go....<P>backwards! The excess amount of air, in high turbo applications, will go backwards and slow the spin of your turbo or reverse it. I'll even go off of what Maldo said. This is going to be pretty broad so spare the specifics:<P>Let's say you have 22 psi set for your turbo. And it is a huge laggy turbo (something of the T-4 series; I'll say a T-66) These don't come anywhere near full spool until around the 4k in RPM's. And let's say the car is shifting at 7000 RPMS (this would be a **** system if you are shifting at that with a T-4 or bigger turbo, but it will make this easier) Lastly, when shifted, the car drops to...3800 RPMs:<P>Shift at 7000 RPMs<BR>Drops to 3500 RPMs<BR>Starts boosting at 2800 RPMs<BR>Full boost of turbo at 4600 RPMs<P>See where I'm going with this? Eliminate the BOV and shift at 7000 RPMs. You *should* have 22 psi of air bouncing off the now closed throttle plate. When it goes back it will be fighting the psi going forward. But remember, no real boost until 4600 RPMs. So you have, say, 10 psi moving forward with 22 psi moving backwards. In most cases the turbo will either a) Have just enough boost to keep spinning forwards. Or b) won't boost enough in time to fight the backshock of 22 psi. In this case backwards she goes.<P>Trust me palado. You know what you are talking about but you are missing a big concept of what a BOV is for: Making sure your turbo doesn't work harder/moves in a direction you really don't want it to.<P>It should also be said that the worse thing a BOV system could do is leak (I think it's worse than creeping) A friend of mine lost a T-28 powered car because his boost gauge read 18psi even though his turbo was spinning like it was 29 psi.

[pelado]

Sorry, I'm hardheaded and turbos have been around a long time on street machines before BOVs appeared. <P>I'm betting that for most turbos no damage would be done unless you have the boost way up there. Obviously I'm also betting that BOVs are window dressing for all the turbos only running 5-7 psi.