Quick BOV question?

[prelude180]

I'm a little bit confused. What is the benfit of an atomosphric blow off valve if every time it goes off, you loose boost? A recirculating bov still lets you keep some boost. There has to be another benefit besides the audio aspect. Also, in order to run an atmospheric bov, do you need to convert to a MAP sensor?

[ALTRNTV]

When you run atmospheric, all the air is being released to the outside. As that's happening, fuel is added into the engine without that air being combusted with the gas. That makes your car run rich, and you lose MPG that way. It also makes some cars stall because of the uneven mixture.

When you run re-circulated, instead of the air being vented to the outside, it goes back into the intake tube. Save more gas that way, and your car doesn't stall. You still get the BOV sound, but not as loud.

[Frappe]

Is that to imply that there is not a benefit?
I'm curious about this too. Is there a benefit to atmospheric in certain situations/applications?

[s13silady]

iirc, there isnt really any good things to having an atmospheric blow off valve besides the sound...you run rich after every shift, so if your car is rich already then you will backfire... you'll more likely to leak boost, you might stall out because of the lost air, and your turbo lag will increase..

[skatanic28]

you can run a blow-thru mafs or use the decel-air function on the safc if you really want to vent to atm. i was originally planning on doin that, but now just for simplicity and troubleshooting im gonna recirc.

[KoukiMonster]

are there only certain bov's that can recirculate? or is it all of them with the necessary equipment?

[prelude180]

Maybe I'm wrong, but isnt the recirulate just postponing the problem. The whole point of the bov is let out air so the turbo isnt boosting into a closed throttle. But the recirculate is sent back into the intake before the trottle. So if your turbo is spinnnig really fast, you still have the same problem, because it is pushing more air into a space closed off by the throttle, the recircualte is just adding a little more space, but not elimnating the problem? Am I misunderstanding something here?



Also is there any benefit to switching over to a MAP sensor and then running atmohperic BOV? Is this more benefical then say running a MAS with a recirculate BOV?

[KoukiMonster]

well we run a maf so its beneficial to recirc.

[prelude180]

yes, but I was wondering if there are any major benefits to converting over to a MAP sensor and using an atmospheric bov, compared to the regular recirculate/ MAS sensor setup?

[Distorted]

yes, but I was wondering if there are any major benefits to converting over to a MAP sensor and using an atmospheric bov, compared to the regular recirculate/ MAS sensor setup?

MAF sensors as you know run off air, so logically if there ins't a continuous volume of air, you have a problem. Using a BOV with a MAF frequently harms your car's performace on the whole. A MAP sensor runs off pressure, so regardless of the volume of air as long as there is till pressure, you're car runs fine. This is grossly simplified but i'm not qualified to teach a physics class. think of it this way, you vent air on a MAF system and the car goes "where the fuck is the air, shit, give it fuel to keep it going." So you backfire and it sounds cool and the BOV goes "FOOOOSH" and you're happy, but slowly your hurting your motor and in turn your walet. Now think of a MAP system (this is where my turbo/na honda experience is great), if you vent to the atmosphere, it means nothing to the engine computer, it has no idea what air volume is, it just knows pressure. Your car runs fine, and IMHO is easier to tune because you can go off fine pressure adjustments and compensate very easily for density, but thats just the bulk of my personal experience speaking.

The main answer to your questions is IF you switch to a MAP system, and i CAN be done its just tricky or expensive, you can vent to the atmopshere. If you keep a MAF system, it's better to use a reciculating system. If the sound matters that much to someone, let them vent, if performance is their true concern then they should recirculate. AND almost all BOV's can be adapted or are designed to be used for recirculating, it just means you add a pipe.

[tErbo b00st]

Most people have the general idea but here is really what happens...

The advantage to venting the the atmosphere is that you are getting rid of the hot air in the intake tract. when you recirculate it usually gets recirculated back before the turbo, this air is hotter than ambiant air because it has already been compressed and run through the engine bay. Then you put it back in and it gets recompressed and gets even hotter. As you should know, hot air is an enemy.

Now the disadvantage to running atm is when you are running a suck through MAF. Your MAF reads a certain amount of air going into the intake and records it in the ECU and uses this amount/temp of air to calibrate how much fuel to put in. When you vent the air goes bye bye, but the ECU doesnt know about this change. So it thinks that there is x amount of air and injects enough fuel to run correctly, but the air is not there so too much fuel is injected, aka u run rich. This is where the backfiring comes from because the unburnt gas goes out the exhaust valves and into the exhaust where it puddles up and gets heated enough where it explodes in the exhaust.

Two ways to counter this (AFC settings ect, just make things better. You cant actually fix it). Either change to a blow through MAF, or a MAP sensor. With a blow through you basically just move the position of the MAF to after the BOV. So the air that gets vented never actually gets registered by the ECU because it is gone before the MAF sees it. MAP sensor works pretty much the same way (in this case). The MAP sensor is generally located in the intake Mani or TB and so it senses the air actually going into the manifold, so any air that gets vented isnt registered. The fact that it registers pressure as opposed to amount of air doesnt really matter (as far as I know).

And yes only certain BOVs can be recir. Most can, but certain ones such as race BOV (Greddy, HKS, ect) and Tial BOV.

So there isnt a Huge advantage, except the sound and the small performance gain you get by not recirc. the hot air. But the more boost you run the hotter the air gets, hence why most high HP cars vent to the Atm.

And that concludes todays class.

[timmybgood]

i have absolutly no stallng issues with my atmosphere bov. occasional backfires though

[prelude180]

How difficult is it to convert to MAP sensor. I know apexi sells a kit for converting, when you pruchase a D-jetro Pfc. Also is it good/bad idea to move MAF sensor after the BOV?