recirculation bov

[Cdaug720]

I have a recirculating bov on my 97 gs-t but i dont have it hooked up into my intake pipe. ive heard different things about it. ive heard from some people that it wont make a very big difference if i hook it up, but i've also heard that it will make a huge difference if i hook it up. any thoughts about this?

thanks,
christian

 

[my dreamt dsm]

There's ton of info. Please read and decide for yourself! Let's just say 99.9% of these cars will run like crap without it or proper mods to support it.

DSM Forums - Search Results

 

[LiquidX]

On a stock system, you have a mass airflow sensor pre turbo. That measures the amount of air going to the motor. Once you have a leaks, either vacuum or boost, the amount of measured air has now changed and is different that what the motor is expecting at a given time.

Boost leaks cause the air to escape making a richer air to fuel mixture while vacuum increases the air in the intake making a leaner air to fuel mixture. Venting to the atmosphere instead of recirculating while on a MAS causes for a brief moment, a rich condition.

If the BOV happens to leak as well then you will have idling issues, bogging, stalling since the mixture would be going extremely lean.

As mentioned, some cars get away with it (more than likely 100% leak free setups) while others just won't run at all.

"Function over form" is the motto, so do things right and recirculate. You will still have a noise if that is why it was done if the first place.

If you truly want to vent then there are a couple routes you can go, you can either get a GM MAF and install it so it is in blow through mode or run speed density. I would opt for the latter as it's a better design.

Korrey, your link doesn't work bud.

 

[Cdaug720]

ok cool. yeah the guy i bought my car from showed me this way to compress the spring in my bov more so that it doesn't bog down after it blows off. but i'm thinking i'll hook it up. i just have this extra pipe sitting in my garage that is designed for a recirc bov. i'll probably throw it on today thanks for your guys' help

 

[jtmcinder]

Sounds to me as if you don't have the OE plastic valve on there. You can't crush the 2G plastic valve to make it hold more boost; it will fall apart.

 

[Ev0Stev0]

Sounds to me as if you don't have the OE plastic valve on there. You can't crush the 2G plastic valve to make it hold more boost; it will fall apart.

yea, make sure your doing the right thing to the right BOV. is it aftermarket? stock? or a stock 1g bov?

 

[LiquidX]

...compress the spring in my bov more so that it doesn't bog down after it blows off...

You were either missinformed or just wrote it out wrong.

The bogging happens from LOOSING air out of the intake system when the valve opens. Adding more spring tension would allow it to remain shut on higher boost settings.

The stock 2g plastic BOV starts leaking IIRC at around 15lbs of pressure. The only way to prevent that from happening is shimming the spring through the outlet hole which I've only seen 1 person do that too as it's IMHO not worth the work.

The 1g BOV can be crushed a little bit to allow it to hold more pressure before it blows open pre maturely.

Again, bogging and stalling will happen when the ECU is expecting X amount of air to spray Y amount of fuel. When X =/= X, the ratio is off but the ECU doesn't know it and then you are left with either too much or too little fuel for the amount of air.

 

[Ev0Stev0]

You were either missinformed or just wrote it out wrong.

The bogging happens from LOOSING air out of the intake system when the valve opens. Adding more spring tension would allow it to remain shut on higher boost settings.

The stock 2g plastic BOV starts leaking IIRC at around 15lbs of pressure. The only way to prevent that from happening is shimming the spring through the outlet hole which I've only seen 1 person do that too as it's IMHO not worth the work.

The 1g BOV can be crushed a little bit to allow it to hold more pressure before it blows open pre maturely.

Again, bogging and stalling will happen when the ECU is expecting X amount of air to spray Y amount of fuel. When X =/= X, the ratio is off but the ECU doesn't know it and then you are left with either too much or too little fuel for the amount of air.

They dont call him a wiseman for nothing.

Conclusion: hook it up how its supposed to be.

 

[jed344]

unless you are guna run SD or gm maf yes hook it up.

 

[LiquidX]

Until you run SD or gm maf then keep it hooked it up.

Fixed.



On another note, if you want one more tid bit of info, keeping the BOV recirculated will also help keep the turbo spooled a bit more in between shifts. If you look in the stock intake pipe, there is a hard plastic tube (if it hasn't been removed) that goes from the BOV return inlet to just before the compressor wheel on the turbo. When the BOV opens, the puff of pressurized air is directed towards the wheel helping it keep it's speed up.

So there are other benefits to having it hooked up as well

 

[jtmcinder]

Somewhat related the above last tid-bit: the rather strange, integrated-into-the-turbo CBV on the recent SRT-4s is aimed at exactly the same issue - maintaining turbo speed/spool - and does it even better than a regular CBV. The downside to how it's done on the SRT-4 is that the recirculated air has not been through the IC, so it's hot.

 

[CrawlinZX14]

I had my bov uncirculated and my car ran fine unless I was at cruising speeds with the stock bov. Because the bov would open at about 3k rpm at say 65 or so and would cause the car to break up. It would bog down a bit as I would get into the throttle until boost kicked in and would close off the bov. I'm going to try an aftermarket bov and see how that holds but I will likely recirculate it until I swap to speed density next spring.

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[sugarfree]

i just don't understand your theory behind recirculation, the recirculation port on the intake is post maf sensor so with the air entering after the maf fuel trim should be irrelevent. I just find it hard to believe that the bov can push enough air to not only overcome the entire turbo and intake piping but to also factor in that there is an open hole right there aka air filter with the throttle plate shut and the injectors in closed loop whats the purpose in enrichening the mixture anyway? just my thoughts but then again i'm another ex honda guy

 

[LiquidX]

i just don't understand your theory behind recirculation, the recirculation port on the intake is post maf sensor so with the air entering after the maf fuel trim should be irrelevent.

Incorrect, every bit of air that is entering the system (which should be 100% leak free) comes in through the intake filter and then through the MAF to be measured. Any air coming in after the MAF is unaccounted for by the ECU so you'll either
A. Have too much air from a vacuum leak (sucking in air) post MAF causing a too lean condition.
B. Have not enough air causing too rich conditions which would happen with a boost leak (pushing air out) or when you vent improperly.

I just find it hard to believe that the bov can push enough air to not only overcome the entire turbo and intake piping but to also factor in that there is an open hole right there aka air filter with the throttle plate shut and the injectors in closed loop whats the purpose in enrichening the mixture anyway? just my thoughts but then again i'm another ex honda guy

Can you explain this better or in a different way. When air leaks out, the ECU isn't making the mixture richer, it's still injecting the same amount of fuel however the measured amount of air that is supposed to be in the cylinders at that time is no longer there since a portion leaked out.

 

[jtmcinder]

You need to separate two issues: the amount of air that's entering the engine right now and the amount of air that will enter the engine at some point.

Nothing short of speed-density will get you are accurate value for the former. The best that any mass-air-type system can hope for is getting the right value for the amount of air that will enter the engine at some point and hope that the moment-to-moment inaccuracies don't cause too much grief.

As soon as you combine a mass-air-type system with leaks anywhere between the MAF and the engine, then you have neither ... you don't have an accurate measure of air entering the engine right now and you don't have an accurate measure of total air that will enter the engine at some point. This is unacceptable. That's why post-MAF CBVs must be recirculated.

If you really, really gotta have a car that makes silly noises, but can't handle speed-density, then get a blow-through MAF and put it after the CBV and before the throttle body.

 

[sugarfree]

Can you explain this better or in a different way. When air leaks out, the ECU isn't making the mixture richer, it's still injecting the same amount of fuel however the measured amount of air that is supposed to be in the cylinders at that time is no longer there since a portion leaked out.

I'm saying that the inlet from the recirculation valve is after the maf sensor so that any air introduced after that point is unaccounted for my the maf so the ecu will not see this extra air. The throttle plate is also shut when the bov/recirc. valve opens which would mean that the fuel system is in closed loop hence no fuel. All i meant about the air filter was that when the recirculation valve goes off the excess air is more likely to exit backwards through the filter before it would travel through the entire intake system and into the engine (path of least resistance) I just don't understand how the fueling would be different with either a bov or recirculated setup especially affecting the idle quality of the car. It just seems like there would be other underlying issues related to all the things that are blamed on aftermarket bov's and such. I'm not trying to start an argument just curious as to the reasoning behind all this recirc vs bov debate

 

[Cdaug720]

hey guys! i've been real busy with school and work, but i finally got the chance to put in the new pipe and hook up the recirc bov and it runs better than it ever has with no bogging and no extra spring tensioning! i love the way it sounds too. sometime down the road when i have a little more time on my hands id like to install the gm maf, but until i finish school my car has to stay how it is! :/ thanks for the info

 

[WES_393]

I'm saying that the inlet from the recirculation valve is after the maf sensor so that any air introduced after that point is unaccounted for my the maf so the ecu will not see this extra air. The throttle plate is also shut when the bov/recirc. valve opens which would mean that the fuel system is in closed loop hence no fuel. All i meant about the air filter was that when the recirculation valve goes off the excess air is more likely to exit backwards through the filter before it would travel through the entire intake system and into the engine (path of least resistance) I just don't understand how the fueling would be different with either a bov or recirculated setup especially affecting the idle quality of the car. It just seems like there would be other underlying issues related to all the things that are blamed on aftermarket bov's and such. I'm not trying to start an argument just curious as to the reasoning behind all this recirc vs bov debate

When you let off the throttle and the BOV vents back into the intake, the vacuum from the engine draws it back in. Yes, you are reducing vacuum at the MAF, but that's good because you don't need more fuel at that moment anyways. So the pressure that is vented is just fed back into the engine. Since the ECU already counted this air, it assumes it will get to the engine eventually via recirc tube and adds the appropriate amount of fuel. If you vent the BOV to atmosphere, the ECU adds fuel for the once counted air (which has just dissapeared) and then adds even more fuel for the new air entering the MAF. This will cause the engine to run rich until it is done adding fuel for the air it assumed was coming from the BOV.

So it's not a problem with aftermarket BOV's, it's just how the intake and fuel system work together on our cars. The ECU uses the airflow it reads from the MAF to adjust the amount of fuel coming into the engine. By bypassing any airflow after the MAF you are throwing the ECU off. That's why boost leaks on our cars cause such a big problem. Venting your BOV to atmosphere is basically a giant boost leak that happens only when you shift.