Open or Closed BOV????

[aking3000gt]

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?

[Twizted_3KGT]

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?

[Thourun]

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.

[Igovert500]

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.

[Twizted_3KGT]

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.

[Gateway]

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

[G35turbo]

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.

[Thourun]

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.

[LandoAWD]

Originally Posted by Thourun

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.

[k3smostwanted]

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.

[Thourun]

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.

[k3smostwanted]

Originally Posted by Thourun

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...

[Igovert500]

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.

[k3smostwanted]

Originally Posted by Igovert500

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???

Originally Posted by Igovert500

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.

[Thourun]

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