Open or Closed BOV????

Ight im new to the turbo world... sooooo im just wondering wut kind of blow off valve sounds the best on the vr4.... i was looking at the greddy type s and its a closed application.... or the type rs and its a open application.... whats the difference and has anyone experienced problems or would like to share there thoughts about these 2 BOV's?

I can't answer your question but since I have one on the same topic...

When the blow off valve shoots off or w/e it does...is it supposed to stop the engine RPM's from going up?...cuz when I was driving the TT the other day I could only make it to like 6000 RPM's and it would go off and the whole car would jerk and i'd have to shift to get boost back...is that normal?

I would guess thats the wastegates Twizted, I think thats what they're for. The BOV goes off when you shift at higher RPMs I think.

OK, some confusion going on here.

First off, I suggest you read the BOV comparison by John Monnin (the link is provided in the FAQ) it will answer a bunch of the initial questions.

Secondly, a bov only vents and releases air when 1 of 2 things occurs:
1) After hard acceleration, boost is built up, turbos spooling..if you are flooring it the air is coming in the intake, going through the turbos, through the intercoolers, and up towards the throttle body to go into the combustion chambers...if you suddenly let off the gas, this intake system is pressurized....to prevent the air going backwards and causing backpressure on the turbo compressor wheels, the BOV opens so that excess air can escape...not if it is an open-loop BOV, that air gets released under the hood. If it is closed-loop, that air is redirected back into the intake tubing (before the turbos).

2nd case scenario is if you are flooring it and you shift...same essential thing happens as if you had just let off the gas...the throttle body closes, the pressurized air has nowhere to go, and it is vented by the BOV.

Twizted, from what I understand, you are saying that while you were still giving it gas, the air was released...this shouldn't happen. The air should only be released if you let off the gas or if you shift...if pressurized air is being released while you are still accelerating...then either the wastegates or BOV are leaking.

Yeah I was flooring it and it would actually stop me and I had no choice but to shift or go nowhere basically...btw it wasn't my car, so i'm not too worried about it ;)

is it possible that he had some mods that would make too much power and pressure for the BOV while accelerating? It did it in each gear from 1st to 3rd (didn't go higher than that). I mean idk how a stock TT feels, but that thing felt ridiculous...but it looked stock except cosmetics.

i've been told that closed loop is better than open loop.

Hey Igovert500 which is better, you said the open-loop BOV, that air gets released under the hood. If it is closed-loop, that air is redirected back into the intake tubing (before the turbos). Is it better to go back to the into the intake or if its just released under the hood. I have the Turbo XS RFL BOV and i am just wondering if i went with the wrong proudct.

Thx.

He's probably just gonna tell you to read the FAQ, which I think I'm going to do since I will be entering the complicated world of the VR4 soon. I'm going to venture to guess they're about the same in terms of performance. The open will sound off louder though so people love that, pluss it causes the engine to run rich for a second after it lets off (which can make your exhaust flame a little out the back if your catless) because the air that was let out of the presurized system is allready acounted for by the MAS so the ECU will inject too much fuel for a second.

He's probably just gonna tell you to read the FAQ, which I think I'm going to do since I will be entering the complicated world of the VR4 soon. I'm going to venture to guess they're about the same in terms of performance. The open will sound off louder though so people love that, pluss it causes the engine to run rich for a second after it lets off (which can make your exhaust flame a little out the back if your catless) because the air that was let out of the presurized system is allready acounted for by the MAS so the ECU will inject too much fuel for a second.
Right on. Reciruclation will also help you to not stall out when coming to a stop, and othe side effects of an open-atmosphere BOV.

In regards top closed-loop, that is a term for O2 sensor readings, etc...just to avoid any confusion.

yeah, basically what you guys are calling a closed-loop BOV is a recirculation valve which is the best kind of BOV because it doesnt waste good air that the motor has already pressurized. but then that pshhh...sound isnt quite as noticeable if you can hear it at all. most turbocharged cars come with a form of recirculation BOV of some sort stock.

the problem stated above about with the BOV "blowing off" while accelerating, it sounds like the BOV wasnt able to keep the air pressurized long enough...whether it was a spring type BOV that the spring was not strong/stiff enough. either way it soudns like the BOV isnt rated at the amount of boost he was running.

a closed-loop BOV is a recirculation valve which is the best kind of BOV because it doesnt waste good air that the motor has already pressurized.
So closed loop BOVs redirect the pressurized air back into an area where its presurized? That dosent sound right, it wouldent work then. I bet they route the air in between the turbos and the MAS.

I bet you ment that the air goes to where it was not pressurized but then the pressure is still wasted for the most part, I'd take the pshh and immediate release of pressure, flames are a bonus.

So closed loop BOVs redirect the pressurized air back into an area where its presurized? That dosent sound right, it wouldent work then. I bet they route the air in between the turbos and the MAS.

I bet you ment that the air goes to where it was not pressurized but then the pressure is still wasted for the most part, I'd take the pshh and immediate release of pressure, flames are a bonus.

oh yeah, i would take the open atmosphere BOV any day...

what i meant was a recirculation BOV just puts that air that would be "blown off" into the atmosphere, and puts it back into the intake air flow. this type of setup works well with air boxs of some sort because then you have a bunch of air that has usually been cooled down (compared to what is normally in the engine bay) right in your air stream...
for example, when you shift, the air is blown into the air box then when you go WOT after you release the clutch, you have that air sitting there in the air box ready to be ingested once again. then their is hardly any air wasted...

what i meant about the pressurized air, if you had it set-up right, you could divert the air directly in the intake piping. so when you punch the throttle again after shifting the air would almost be forcing itself back into the air stream, this can cause the engine to get the air alot faster than it pulling the air out of the atmosphere by itself.

anyways, just get the open atmosphere...as long as the air is getting out of the piping your fine. that is the sole purpose of a BOV, so whatever. you dont want more lag than you already have...

I'd say go closed loop any day. Running on the lean side = good for performance. Open-loop bovs cause the car to run a bit rich after shifts...
Plus recirculating bovs, put the air back behind the MAS, directly back into the airstream (not into an airbox) and this causes boost to be regained much quicker after a shift. Lastly, with an open-element intake, you can definantly hear a recirculating BOV. It wont be as loud, but if it's going to cost you $200, I'd rather get something more performance oriented than a noise maker.

I'd say go closed loop any day. Running on the lean side = good for performance. Open-loop bovs cause the car to run a bit rich after shifts...

hmm...how is running on the lean side good for performance???


Plus recirculating bovs, put the air back behind the MAS, directly back into the airstream (not into an airbox) and this causes boost to be regained much quicker after a shift.

yeah, stock units just put it back in the airbox because the manufacturers dont want to run a FI car lean. lean + FI = detonation, which means less engine life.

Lean, rich... pshhh, its all about stoichiomitry, and I think lean is closer than rich so it is better for performance per unit burned.

Lean, rich... pshhh, its all about stoichiomitry, and I think lean is closer than rich so it is better for performance per unit burned.

i dont know if lean is better for performance or not but i do now id much rather have my car run rich than lean. oxygen and fuel combined cause combustion which causes power, so i dont see how more than one of the other without more of the other could help with performance. but maybe im missing something...all as i know is that i personally would much rather run rich than lean but the type of BOV you use isnt going to make a huge difference in either.

Stoichiomitry is how perfect a chemical reaction is, in this case oxidization. Say you have a gallon of gas, now if you are able to tune it so that its right at the lean limit you are burning a higher percentage of that gallon than if you decided to play it a bit safer inject less oxygen than is needed for a complete burn some of the energy is wasted and not all the bonds are broken so it just goes out the exhaust. Its all about tuning the burn to the point just before you would encounter "spontanious" combustion due to compression, thats when you get the most efficient burn and the most power out of the engine per amount of gas injected.

The best performance comes from running as lean as possible without knock.

2) The airbox is before the MAS, the recirculation tube is behind the MAS. If it dumped the air back into the airbox, it would be just as worthless as venting to atmosphere...it recirculates it back in behind the MAS, because the air has already been accounted for, therefore the ECU already expects the air to be there and is sending the appropriate fuel...if the air is vented to the airbox side of the MAS, then the car would run rich (just like venting). Rich = unburnt fuel (this is why you might get the flames out of the exhaust) Rich = not ideal performance.

Stoichiomitry is how perfect a chemical reaction is, in this case oxidization. Say you have a gallon of gas, now if you are able to tune it so that its right at the lean limit you are burning a higher percentage of that gallon than if you decided to play it a bit safer inject less oxygen than is needed for a complete burn some of the energy is wasted and not all the bonds are broken so it just goes out the exhaust. Its all about tuning the burn to the point just before you would encounter "spontanious" combustion due to compression, thats when you get the most efficient burn and the most power out of the engine per amount of gas injected.

hmmm...sounds good. whatever works, right...i still would rather run rich. too chancy. this is why performance FI cars come running on the rich side, stock. so you can get the most life out of your 300hp twin-turbocharged motor. when your running boost on a motor like these you have to be careful on what you do. if you get a boost spike and your already running on the lean side, it could be all over for that motor. im not sayiong this has any relevance to BOV's, just saying.

Is the stock BOV worse in terms of performace than the aftermarket ones? I would guess so because spending $200 for a noise is rediculous.

Is the stock BOV worse in terms of performace than the aftermarket ones? I would guess so because spending $200 for a noise is rediculous.

well i dont know if aftermarket ones serve any significant useful purpose when the engine is stock and you are running stock boost. but when you raise boost levels in the car just a little, the stock BOV is usually not capable of handling anything more than the stock boost setting. if it cant handle the boost then it will start leaking your boost before you let off the gas. this is where aftermarket pieces are needed and also why it is important to buy a BOV that fits your requirements. soem BOV's have different stiffness of springs and what not to control the boost release and how much it can hold. i think Tial's are set-up this way...

The stock one is POS plastic recirculation valve. At stock levels, it works, usually (mine started leaking at 12psi) but an aftermarket closed-loop one will help your turbos respool faster(so the car seems faster, although it really isn't). So yes they are a bit better, but at stock boost levels, the stock one is fine if it isn't leaking like k3s said.