BOV re-circulation kit

[WDRacing]

if your BOV leaks you'll stall at idle speed...also, when your bov acually vents pressure to the atmosphere, it creates an over rich condition, causing bad plugs and loss in power as well as stalling, there is no need to run open bov's unless your going for the "hey I've got rice here" look...

WD

[sultan]

why does venting the bov cause car to run rich? your MAF reads how much air is being sucked in, when you close the throttle quickly and the bov vents the air that the MAF measured is vented out, but the computer doesn't know that. the computer thinks it's getting more air than it is, and therefore gives too much fuel and runs rich. that's why you recirculate the bov back into the intake after the MAF. i think an air/fuel controller will help if you really want to vent it. venting the bov can also cause your car to stall.

[Flamereka]

Well you have to imagine how the ECU is programed. The air is being pushed in at a certain rate , and the proper ratio of fuel is being injected also. When the BOV vents air it releases some of the air going into the engine. The car still ends up getting the same fuel as it did before though. So you end up getting a richer fuel ratio.

I don't even like the idea of a BOV my self except the fact that they may help save your turbo from compressor surge.I don't recall seeing them on any turbo drag cars since they would cost them some time getting up the boost again.

I also have a question i'm going to make a main thread. "How dangerous is compressor surge to your turbo"

[sultan]

quote from another site:"The MAF sensor is used to determine the amount of air the engine is using so it can deliver the appropriate amount of fuel. In a car with a MAF sensor, when a BOV vents, air is escaping from a closed system. This air has already passed through the MAF sensor and has been measured, and the computer doesn't know that this air never made it to the engine. This will cause a brief rich mixture as the computer will still deliver the correct amount fuel dosage based on the amount of vented air."basically you're still bringing air in, it's measured by MAF (which is used to determine how much fuel to give), but a lot of it goes out the BOV and never reaches the engine, so the car gets too much gas.

[Exar-Kun]

just stick the MAF in front of the throttle body and be done with it.-chet

[WDRacing]

It's not a hard concept to grasp really, your MAF has registered say 21 parts of air going into your engine, so it adds 21 parts of fuel...when the BOV vents...the air that the ECU has already calculated has been removed. So the ecu isn't adding more fuel, your just removing the air...get it???

WD

[C-Kwik]

I don't think you understand what happens. Your ECU has no idea the BOV is letting this air out. When you vent out the BOV air, the ECU will still think that the motor is getting all the air the MAF is reading. So it will add the appropriate amount of fuel for the amount of air the MAF is telling the ECU it is getting. But since the motor is not actually geting all that air, you will have much more fuel than is needed, therefore you will be running rich. It's not a huge problem except at idle when you immediately come off of boost, which is when the engine would stall due to the overly rich mixture.

[Exar-Kun]

most piggyback-fuel computers have a compensator for that...-chet

[matt0941]

Chet, how would the PB know? Say that you did program it with the some option saying you are running a BOV. How will it know when the BOV is about to vent and anticipate this without spraying more fuel?

As for 98KA24DET, if you don't get this concept by now... jeesh. But if you don't understand the other replies: BOV comes after the MAF. MAF thinks all of that air going through it is going to continue undisturbed, so the ECU adds more fuel to the combustion chamber; but does not know the BOV vented air to the atmosphere. Hence: too little air, too much fuel.

[Exar-Kun]

usually the piggy back will get a loss-of-boost signal, and correct for it, I know apex-i's new AFC2 and HKS' both have similar compensation options.-chet

[Nismo1182]

Chet, how would the PB know? Say that you did program it with the some option saying you are running a BOV. How will it know when the BOV is about to vent and anticipate this without spraying more fuel?

As for 98KA24DET, if you don't get this concept by now... jeesh. But if you don't understand the other replies: BOV comes after the MAF. MAF thinks all of that air going through it is going to continue undisturbed, so the ECU adds more fuel to the combustion chamber; but does not know the BOV vented air to the atmosphere. Hence: too little air, too much fuel.

Thats what everyone is saying but he was asking since the turbo does not stop turning while shifting there will always be air in the intake. How would the ecu handle this?

[matt0941]

Gotcha. But just to clarify for others as it is a wide misconception; shifting is not the only time the BOV vents to the atmosphere. The BOV vents when throttle is shut and pressure resides. So if you step on the gas, the compressor starts spinning, compressed air is running through - and THEN you let off the gas the BOV vents. This is the reason you will only hear the BOV vent when someone is dragging, because they are constantly on the gas except when they let off (vents now) in order to shift. Very basic stuff but still worth mentioning.

[WDRacing]

The newer PB's have idles stabilazation, it meters the unstable MAF voltages. Works really well from what I've seen. The HKS SAFR seems to work with no problems with several different types of BOV's. I've never used the new SAFC II. But I imagine it works just as well.

WD

[Turbo240project]

I don't know about the AFC-II but the S-AFC I's deceleration feature doesn't work on cars with a MAS.

[matt0941]

The newer PB's have idles stabilazation, it meters the unstable MAF voltages. Works really well from what I've seen. The HKS SAFR seems to work with no problems with several different types of BOV's. I've never used the new SAFC II. But I imagine it works just as well.

WD

Ok now you are confusing me. So it monitors the MAF, but if the MAF comes before the BOV it would still have no way of telling that air has been vented. So how does the PB account for this?

[WDRacing]

It compensates for eratic MAF voltage readings, check out the HKS SAFR on the HKS website, it explains it....

[drifties151]

if you're hell bent on running an open air BOV... run a "blow through" setup. position the bov on the intake side of the turbo... and position the MAFS on the cold side of the intercooler. this will eliminate any problems of measured air escaping before it reaches the TB. A couple guys at Unstable Hybrids run his setup and they havent had any problems. For some pics on their setups go to http://www.unstable-hybrids.com. for some reason the board isnt letting me post up some easy to read diagrams of the setups so if anybody could help me out w. that it would make things a little easier to explain.

[groundhogday1976]

The "blow through" setup sounds like it would work, but don't you want the BOV close to the throttle body? If the air bounces off the closed plate on the throttle body and has to travel back so far, wouldn't that keep the turbo from spooling up as quickly after a shift due to the air colliding w/ the new air that's coming in?

Another thing to add to the topic: some BOVs open under vaccum but shut under boost. If you have one of these, you'll have the rich condition at idle everyone's talking about because if you're venting to the atmosphere, counted air is being lost. And under boost conditions, even though the turbo is still spinning and air is coming in between shifts, the air you vented has still been counted and the ECU doesn't know anything about it. It still adds the proper amount of fuel for the amount of air the MAF counted whether that air reaches the combustion chamber or not.