In another thread, rolling_trip posted this: Which spawned some questions. SS/Doug/others with tuning knowledge, just how DO you tune for a BOV? If the air is dumped out after the MAF meters it, how would you compensate for this with a tune? With my limited knowledge about FI setups, it seems that unless you're metering after the BOV, it'd be damn difficult to properly compensate for the arbitrary amount of air going out of the intake tract.
As far as I know , and hopefully the other guys will chime in, unless you have a blow through setup you cant tune around it, since youll run rich in between shifts and only then. Resulting in fouled plugs eventually and worse if you have a stock up and down. USDM WRX's cant be tuned for it because that air its venting isnt metered by the MAF. So regardless the ECU has no idea its not getting that air back into the intake.
Take a chill pill, dude, nobody's out to make fun of you. You suggested starting a thread for it and I'm actually curious to see what the tuners do to handle BOVs. The problem I'm having with the atmospheric ones is that the air is metered accurately at the MAF, before turbo and BOV and all that. The ECU doesn't need to factor it in since it's air that's already been metered that is returning into the intake tract post-MAF. Basically, it's a 'closed system' of sorts in that air that is measured WILL go into the engine. When using an atmospheric BOV, some of this metered air will leave the system, and short of the ECU having some way of correcting for this 'missing' air I can't see how you could avoid screwing up the mixture temporarily. C'mon, somebody help us figure this one out.
We're on the same page, but I keep hearing that BOVs can be handled through tuning (just go look at any WRX forum and you'll see it stated over and over again) so wanted to get the final word from somebody who actually does tune these beasts.
i dont think that was his intent at all... you brought up a very good point and i for one am interested in finding a solution obviously the ECU can't magically add more air but could it be possible to have a lookup table that divides the measured amount of air by some factor right after a shift? u dont need to add more air... theoretically u could lean it out some by taking away some fuel too
Either that or relocating the MAF post-BOV, or going away from a MAF metering system altogether... but those seem a little extreme. Your lookup table would probably have to take into account RPM and boost pressure. Doubt such a thing exists in the ECU, but it's an interesting concept.
Any way to take out the assumption that the air is returning and just have the meter do it's job? Seems to me that the meter should not be assuming that air is coming, rather it should be measuring how much air is passing at any given time...I don't want MY mass air making assumptions!!
Well, the meter sits before anything else, like this: MAF---turbo---intercooler/BOV--throttle body/intake The MAF meters every bit of air entering the system. The assumption being made is that the air that has entered the system REMAINS in it. The meter is doing exactly what it's designed to do.
What point does the BOV recirculate back to? Is it back into the intercooler? Any way you could take out the assumption though? Seems like there ought to be some way to recalibrate for this. I mean a pro-tune should be able to deal with it no?
It recircs back to just before the turbo. The problem is that the amount of air leaving the system via a BOV can't really be easily determined. As long as the system remains closed (recirc) the MAF metering is 100% accurate. When you dump out some air it screws the entire process up. In other words, there's no MAF equivalent that meters how much air goes out of the system... and therefore the ECU can't compensate for it. At least that's how I look at it.
good point... that will take us away from my idea of a lookup table... if u cut fuel too much, u might run too lean... better too rich than too lean
just got off the phone with SS... he said its a mechanical issue and u cant tune around it he was a little pre-occupied tuning in tampa but will probably chime in on this when he returns to ATL
That's crazy...I've also heard that you can tune for it as well....I guess I'm glad I didn't follow that advice and went back to recirc anyways...I'm glad this was posted up!!!
theoretically it runs rich but i believe its for a VERY short time... maybe its too short to really matter i saw an STi that kingpin built here in dallas... fully built block with a gt35r and they have a custom recirc line :bigthumb:... i think thats primarily to keep that turbo spooling since he autocrosses with it
I believe any aftermarket bov with the ability to recirc will be louder than stock. iirc, forge makes a full recirc valve to replace and hold more boost then stock. If you guys really want the sound get an intake. This increases the sound of the stock valve a lot, plus you can get tuned for adding an intake. I've talked to many tuners, and 95% of them say you cannot tune for a bov. The other 5% say that there are ways to tune around it to make it not as bad as running it w/o a tune, but still no way to fully compensate for it. If you are running enough boost to warrant the use of a bov, and dont want to mod the stocker to hold more boost, then get a tial bov. They are the only one to my knowledge to actually be able to hold the extra boost.
Just out of curiosity how much will the stocker hold? I am not running an aftermarket turbo, but I am running cobb stage 2 specs...I know this raises the boost some. Any chance that the stocker is getting upset with this and dumping?
Well, here is the way I think it goes step 1: The BOV opens its when the throttle is closed. step 2: when the BOV opens the air goes back into the intake system after the MAF, so the MAF doesn't necessarily record the air in there. step 3: the throttle opens and the turbo starts applying pressure again. This is the period where the intake charge would be rich IF the BOV is venting to atmo. Basically, the BOV helps keep the turbo spooled, and helps keep pressure up in the intake system before the throttle plate. Pressure needs fuel when the throttle is opened. The ECU knows this, and supplies fuel accordingly for the air that is supposed to be there, but has not been metered cause its bypassed the MAF. Take that air away, and the car is supplying fuel for air that is supposed to be there at the begining of the gear run. Solution: remove the extra fuel that is supplied before the turbo actually spools. This entire post is a brain dump of what I know. Thanks for listening.