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Discussion Starter #1
Hello all,
Thought I would take a crack at answering why aftermarket BOV’s cause “problems” with stock cars etc. This picture was taken from Garrets turbo site and modified to show how stock turbo cars (most anyway) read air measurements. Sorry I was bored and decided to try to contribute to the site but I'm far from an expert. :D Maybe now you won’t have to answer this question every 3 minutes. After you read this also you’ll understand why when people say “I’ll get a BOV to fix the boost creep issue” they are incorrect and that will not fix the problem.

A lot of cars have a “MAF” (Mass airflow sensor) Pop the hood and it is right after your intake (shown here as a red cone) this is what reads how much air your intake sucked in. I will use generic numbers for this just to illustrate what I am talking about. If your MAF reads 10cfm of air coming in, your turbo compresses that and when it reaches your cylinders the computer adds fuel for 10cfm. No sputter and you can clearly see the path in the picture. Your car runs nice and works fine during shifting etc.

After market BOV’s work differently since there are 2 main kinds, vent to atmosphere and recirculating. We’ll talk about the ones that everyone wants first, vent to atmosphere (for that cool PSSSHH sound!)

You’ve installed an aftermarket (Vent to Atmosphere) BOV:
Look at the drawing, when the MAF reads 10cfm coming in your turbo compresses that, your computer adds 10cfm of fuel and all works well. Now when you shift things get crazy, your car bucks and it doesn’t run right usually and this is what happens:
When you shift your throttle plate closes, there is 5cfm stuck between the throttle plate and the turbo, the job of a BOV is to relieve pressure on the turbine so the air doesn’t slow it down since its now running against the blades. A stock BOV will recirculate the 5cfm BEFORE the turbo but AFTER your MAF as in the drawing so your blades don’t slow down. The computer then knows/reads 5cmf + the next 10cfm that you sucked in again = fuel for 15cmf of air next time you press the gas. Remember you now have an aftermarket BOV, which means you DUMPED 5cfm of air (that cool PSSHH sound) instead of recirculating the air like stock, so now the computer thinks to add fuel for 15cfm that your SUPPOSED to have but really you only have 10cfm (15cfm – the 5 you dumped for the PSSHH sound) so your car bucks, acts funny and you get lousy gas mileage. This is not the fault of the BOV this is the way your stock computer gets its reading for the air charge coming in, there is no “fault” in this and there are ways around it which I’ll get to in a second. This is also why typically there is a DECREASE in performance when going with an aftermarket BOV with stock MAF's. This does not affect all cars as severely as others since there is alot of variables and also in the way the stock computers work (its not this simple :D)

Recirculating BOV’s:
This is your stock BOV, this work by simply keeping that 5cfm you were going to dump and pushing it back before the turbo but after the MAF sensor. (Note the drawing)

To fix this issue, and/or use a vent to atmosphere BOV with no issues you need to read incoming air other ways like with a VPC (Vein pressure converter) which read air differently and typically closer to the throttle body, that way you can dump all the air you want and the computer only see the air coming in right before the throttle body thereby adding the correct fuel all the time. Stand alone computers also use things like MAP sensors and they almost all get rid of the stock MAF sensor for more accurate readings, this is why people with aftermarket computers can usually use BOV’s that vent to atmosphere with no problems.

Spring vs. Pressure/Vacuum BOV’s
Very quickly a lot of aftermarket BOV’s use a spring to hold the valve closed. Ever watched a movie about a submarine and seen it flood with water? The sailors all rush to close the door on the incoming water (pressure from your turbo) when they close it the water doesn’t come through (but its pushing on the door) that is the springs job, to hold that door closed, when enough backpressure forms the spring opens and releases the air and then shuts the door again. When the spring gets old or isn’t strong enough it cant close the door (or cant close it tight enough) and you get leaks, that’s why some BOV’s have a bad reputation for leaking boost.
Other BOV’s like the HKS BOV use pressure/vacuum to snap the door shut from a source typically like your manifold so the more boost the tighter they seal (so they don’t leak). Think of the sailors except the door is on the other side so the water pushes the door closed, more water, tighter seal, when you shift the pressure on the sailors side pushes the door open, releases pressure and then the door snaps shut as you build boost again. These BOV’s are typically seen as being superior to spring design’s and are considered to react A LOT faster than typical spring style BOV’s since they use pressure and vacuum (like a Boost gauge uses to react to boost increase/decrease quickly and accurately).

Sorry for the oversimplification I just know that on the MR2 boards I used to answer this question 1000x’s a day and this is the easiest way to explain it. Here’s hoping I get my STI soon since I just sold my MR2 for it. :D
 

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Who's Silver STi.....

so i should not buy the worx tuning bov with the sweet wrinkle red finish?
damn.....
although i believe i could set it to 100% recirc... which would in essence cost me $200+ just to have the cool finish, and zero "pssssh" noise.
 

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Discussion Starter #4
*Personally*
I dont know about this BOV and if it can be set both ways but a stock bov (I know for a fact on the MR2) was by far one of the best performing bov's over aftermarket systems. Those that prefer function over *bling* typically dont swap out a stock bov while still on the stock computer.
If you want to hear your BOV you can do the resonator mod so it will be louder and/or (I have not seen the connection on the stock bov on the STI personally) but on my MR2 when I swapped to a larger turbo it came with a METAL return hose/pipe for the stock BOV back into the intake, this made the BOV very loud inside the car :) Best of both worlds.
 

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Re: Looks like Christmas....more of an opinion

Thanks for the explanation. Maybe that's why aftermarket BOVs are know for melting pistons as the increased fuel component overheats the engine, thusly meltdown.

Quick question Silverbane, as it pertains to shifting techniques with turbo vehicles, are there any recommended or discouraged approaches to power shifting? Curious if I leave my gas pedal slammed through shifts, will the load cause any issues?
 

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Is it really taht serious? To melt your pistons with a BOV? I know oyu might run rich, but some people dont even run rich enough to backfire or anything. So I dont know how it'd be so serious you'd be melting pistons? or maybe Im wrong?

Robert~
 

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Discussion Starter #7
jpsti said:
Maybe that's why aftermarket BOVs are know for melting pistons as the increased fuel component overheats the engine, thusly meltdown.

Quick question Silverbane, as it pertains to shifting techniques with turbo vehicles, are there any recommended or discouraged approaches to power shifting? Curious if I leave my gas pedal slammed through shifts, will the load cause any issues?
Actually more fuel in the cylinder will cool the cylinder down more than raise heat, although as we all know running rich = bad performance but that is one reason why the less fuel you have (Running Lean) leads to higher EGT's. I doubt BOV's themselves cause this issue unless the car was already running with a bad A/F mixture already and this just added to the issue. *shrug*

As for powershifting I would be more inclined to belive it will damage your transmission (or syncros) more than it would your engine unless you were bouncing off the limiter, but I would not be the expert to ask on that, that would just be my personal thoughts on the subject. Sorry I cannot accurately answer that question although I'm sure someone else would know better than I. :D
 

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Actually more fuel in the cylinder will cool the cylinder down more than raise heat, although as we all know running rich = bad performance but that is one reason why the less fuel you have (Running Lean) leads to higher EGT's. I doubt BOV's themselves cause this issue unless the car was already running with a bad A/F mixture already and this just added to the issue. *shrug*
YA! Thats what I thought... I thought that is why EGTs are hotter when lean and colder when rich... I figured you might lose 1-2hp, but to some people its worth it. I hopefully will get to pick up another WorxTuning this time with the LOUD BOV ring and such :). Very nice product. Also all BOVs arent the same... some are dual stage, single stage, some have different ways of releasing the pressure, some have a tiny inlet hole, some have a huge inlet hole... i dont think you can put one theory over all BOVs, but I will agree that maybe you'll run a little richer on shifts, but as long as you're not like backfiring or anything I wouldnt think much of it (as WorxTuning says that their design helps with holding RPMs between shifting, making the power transfer smoother and puts you more in the "Sweet spot" range when shifting. So maybe that 1-2hp loss is made up with better shifting and more precise shift changes.)

Robert~
 

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Discussion Starter #9
staticx313 said:
Also all BOVs arent the same... some are dual stage, single stage, some have different ways of releasing the pressure, some have a tiny inlet hole, some have a huge inlet hole... i dont think you can put one theory over all BOVs, but I will agree that maybe you'll run a little richer on shifts, but as long as you're not like backfiring or anything I wouldnt think much of it (as WorxTuning says that their design helps with holding RPMs between shifting, making the power transfer smoother and puts you more in the "Sweet spot" range when shifting. So maybe that 1-2hp loss is made up with better shifting and more precise shift changes.)

Robert~
True, I was just trying to generalize why this problem occurs since regardless of how the BOV releases the pressure the same thing still happens and their end result is the same (measured air escaping)

I'd like to see WorxTunings explanation of how their BOV helps to hold RPMS since the BOV has nothing to do with RPMS directly, especially since the BOV is isolated from the engine by the throttle plate; unless they are speaking about the speed/reaction of the BOV which again I doubt that it can come close (at best can be equal to) a stock bypass valve. Can you link me to some information on this Robert? If i'm wrong about the way their BOV functions I'd like to correct myself.

*edit* I found their website and read what I could on their bov, unfortunately I did not locate much information. I'm not a product basher, I used to have the HKS Super/Dual Dragger on my MR2 due to its sound/looks at the cost of its weight instead of a lighter exhaust fully knowing its pros and cons. Having said that, I dont see specifically how the BOV (other than its advertised speed "Rapid air evacuation" can help keep up RPMS over any other BOV, but it does "look" like a very high quality, spring operated BOV. I am also far from the last word on a product and if its good or bad. Being desinged for the WRX (STI?) I'd assume it would perform well on the vehicle especially when used to reroute the air back into the intake. (although I personally believe that a spring loaded BOV could only perform/react as fast as a stock bypass and not any faster)

Thanks
 

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Also silverbane I understand waht you're saying and Im not bashing you or downing your review. Your review was great and makes 100% sense and I thank you for it, I was just stating some facts :). I will try to find WorxTuning's comments, but that will be difficult. I remember them saying that it helps hold between shifts (the pressure seems to be relased - in their vids - slowly rather then a quick pshhhh, so maybe they mean they hold some pressure so its not slamming the turbo with negative force (or compressor surge, or whatever you wanna call it)? Anyways nice review and sorry I couldnt be of more help. maybe you should email them?

Robert~
 

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Discussion Starter #13
Radio Shack Online

ACK!
Staticx313, I didnt think you were bashing anything, I expected and hoped for some questions in case someone needed some clarification, its all a discussion, like things should be done on forums, not yelling :)
On the MR2 board alot of people are "older" since the MR2's are getting up there in age, and information is shared and questioned (in a good way) all the time. When I asked for a link, i really did want a link to read on what they wrote, if I'm wrong on a subject or new information is provided i WANT to correct myself, too much missinformation is spread about cars as it is. (MY Type R is [email protected] phowahz 'cuz Import tuner said it 3ats v8's YO!)
I hang out here since NASIOC is filled with kids. :D

Oh letting air out slower is not a good thing by a BOV, if it hold the pressure then the air has a chance of slowing the turbo down, you want the air to evacuate rapidly. Oh before I forget alot of other cars, like the old F1's that used turbos didnt use BOV's, some think since they would rebuild engines/swap turbos so often but BOV's on stock cars are supposed to extend turbo life by releaving the pressure of air that is returning to slow the turbine blades down, stock bypass valves work by recirculating air before the turbo (Keeping it spooled up) although personally I have never seen proof that returning air to the turbo shortens the life of the turbo by any large amount. (Just to show you I can stand on both sides of the fence at 1 time :D) although it makes sense that it slows boost building on the next shift compared to recirculated air that keeps the blades spinning in the right direction.

I hope you dont think I was "defending" myself Statix, as you said you did state facts and I was in no way trying to state otherwise :)
 

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lol np i was just stating i wasnt trying to fight you ;) no biggie. I ordered my BOV anyways, but if worse comes to worse, I'll just leave it in 100% recirc. It seemed to make the turbo louder anyways, so that is always a good thing :) Thanks silver!

Robert~
 

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Maybe one of you guys will know - can the Worx BOV be put on an FMIC? I was thinking about getting one, but I also want to get an FMIC (eventually). So, if it won't fit the FMIC, there's not much point in me getting one now.
 

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Discussion Starter #16
I dont know is the my answer :D

but most aftermarket FMIC kits do not have a hole cut out for a BOV already (there is no way they would know if you plan on running one and what angle to place the hole since BOV's are all different in shape and sizes). Typically you can buy a flange/adaptor for the bov, have a good shop weld that onto your FMIC pipe somewhere that the BOV will fit and then you mount the bov to the flange.

Sorry I cant answer 100% correctly since I have never personally seen that BOV mounted directly to any IC's.
 

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elucas730 said:
Maybe one of you guys will know - can the Worx BOV be put on an FMIC? I was thinking about getting one, but I also want to get an FMIC (eventually). So, if it won't fit the FMIC, there's not much point in me getting one now.
You could weld it in, but the only one I think that will do it correctly is the Perrin, as it uses the stock location and such. I think you might have to buy APS's fmic BOV if you buy their bov and so on... or have a shop , like silverbane said , weld it in. Weld in two right by the holes in the front bumper :D, let everyone know whats up ;).

Robert~
 

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Ok stop the presses, the debate is over, [email protected] has spoken: "It is true it runs a tad rich when you shift but it really doesn't affect anything adversely so I'm not really concerned out it. I do offer the Greddy valve if you want it to recirculate." There you have it, if he doesnt find any problems out of the 1000+ dynos he does every day with stock - 1 bolt on part - 1000 bolt on parts - new turbos, then there isnt a problem.

Robert~
 

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I put my stock BOV back on and hit 18.4 PSI and fuel cut off. I have a TBE and intake. I will be going back to my RFL BOV to keep from having this problem again.
 

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?? The bov shouldnt have anything to do with it. The TBE is what is causing it. Having a catback will cause boost creep. Only real fix is porting the wastegate. As I have it too. Kinda funny you mention that though, you might not have boost creep with the RFL because it leaks under high pressure ?

Robert~
 
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