# Blow-off Valve vs Diverter Valve



## VRBehavior (Dec 29, 2006)

Been meaning to ask this for some time. What do you guys prefer or recommend. Which is more dependable and reliable? Is there a certain tier of power in which one is preferential over the other; bOV or DV??


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## morganwelds (Jan 26, 2015)

The factory DV is the only choice. An atmospheric BOV on our cars makes them and most other modern turbo cars run improperly. The factory piston type DV on our cars is good for an absurd amount of boost, and is faster than any vacuum operated valve as well.


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## VRBehavior (Dec 29, 2006)

morganwelds said:


> The factory DV is the only choice. An atmospheric BOV on our cars makes them and most other modern turbo cars run improperly. The factory piston type DV on our cars is good for an absurd amount of boost, and is faster than any vacuum operated valve as well.


Thanks for the input sir! So increased power levels aren't an issue for the DV?


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## kbad (May 26, 2007)

VRBehavior said:


> ... So increased power levels aren't an issue for the DV?


Hey man .. Ditto morganwelds .. Increased power isnt specifically an issue .. The dv's job is to 'release pressure' .. The faster it can accomplish that, the better .. The stock electric solenoid actuator is a solid performer which has been tested to over 400hp with the awe dv and it operates much faster than a vacuum operated one .. However, the 'new improved' stock dv internals are still plastic and can/will crack causing leaks .. The stock dv solenoid should be paired with a simple solid alloy internal like the gfb dv+ that can be tweaked .. Good luck!


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## VirgoPHD (Dec 12, 2014)

Correct me if i'm wrong but doesn't the DV redirect air back into the engine? if so Wouldn't that make the BOV better? Unless running the DV with a spacer.opcorn:


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## [email protected] (Jun 11, 2014)

kbad said:


> Hey man .. Ditto morganwelds .. Increased power isnt specifically an issue .. The dv's job is to 'release pressure' .. The faster it can accomplish that, the better .. The stock electric solenoid actuator is a solid performer which has been tested to over 400hp with the awe dv and it operates much faster than a vacuum operated one .. However, the 'new improved' stock dv internals are still plastic and can/will crack causing leaks .. The stock dv solenoid should be paired with a simple solid alloy internal like the gfb dv+ that can be tweaked .. Good luck!


I completely agree. This is the same exact reason I went with the GFB DV+ on my car. You just can't beat the speed of the solenoid with a vacuum based valve.
The fact that they include the boost equalizing spring is also a plus.


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## kbad (May 26, 2007)

morganwelds said:


> .. atmospheric BOV on our cars makes them and most other modern turbo cars run improperly ..





VirgoPHD said:


> Correct me if i'm wrong but doesn't the DV redirect air back into the engine? if so Wouldn't that make the BOV better? Unless running the DV with a spacer ..


yes .. the dv redirects the 'blow off' back into the turbo inlet, so as not to waste the charged air your turbo spent all its energy on! .. the bov wastes that charged air for the sake of useless noise - it adds no significant performance value .. a spacer adds nothing to a turbo charged system - spacers are used mostly to 'expand' the intake volume so that you can 'hold' more post throttle cold air volume (colder air = higher o2 content = better/larger/cleaner combustion) - with turbos, its a moot point since its all about the size of the turbo and intercooler drain (i.e. pressure exchange rate)


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## The1Bill (Dec 8, 2009)

VirgoPHD said:


> Correct me if i'm wrong but doesn't the DV redirect air back into the engine? if so Wouldn't that make the BOV better? Unless running the DV with a spacer.opcorn:


In general, there are two ways that can be used by an ECU to calculate how much air is entering the engine, as the amount of air entering the combustion chamber dictates how much fuel must be added to attain the right lambda (air-fuel ratio).

The first method is called Speed Density. The volume of air entering is calculated based on the known volume of the intake manifold, the temperature of the air entering the engine (as colder air is denser, temperature correction needs to be performed), and the pressure within the intake manifold. Based on these three pieces of data, the ECU can determine how much air is entering the combustion chamber, and then calculate how much fuel to inject. The MAP and the IAT (Intake Air Temperature) sensors are in the manifold. The air is therefore "counted" in the intake manifold.

The second method is called Mass Air Flow. The temperature of the air is measured before the turbo, and the volume of air passing by the Mass Air Flow sensor. Once the air passes this sensor, it has been "counted".

Once air has been "counted", an amount of fuel is allocated to it. That fuel is injected into the combustion chamber. If air that has been counted does not complete the trip into the combustion chamber, the relative quantity of fuel to air will be too high. In other words, the engine will run rich.

Since we use Mass Air Flow, dumping air post-turbo when the throttle closes will result in the fuel "allocated" to that air to be sprayed into the combustion chamber. This can cause driveability issues, fouled cats, fouled O2 sensors, and a whole host of other issues. Fortunately, most people won't make it past the driveability issues for long enough to do damage - the car will likely run like crap for a moment each time the throttle is closed while the system is in positive pressure (boost).

That is the long winded answer.

TL : DR - If you vent to atmosphere, you'll run pig rich for a moment every time you shift.


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## VirgoPHD (Dec 12, 2014)

The1Bill said:


> In general, there are two ways that can be used by an ECU to calculate how much air is entering the engine, as the amount of air entering the combustion chamber dictates how much fuel must be added to attain the right lambda (air-fuel ratio).
> 
> The first method is called Speed Density. The volume of air entering is calculated based on the known volume of the intake manifold, the temperature of the air entering the engine (as colder air is denser, temperature correction needs to be performed), and the pressure within the intake manifold. Based on these three pieces of data, the ECU can determine how much air is entering the combustion chamber, and then calculate how much fuel to inject. The MAP and the IAT (Intake Air Temperature) sensors are in the manifold. The air is therefore "counted" in the intake manifold.
> 
> ...


So no need for a spacer then is what I'm gathering from all this. I was concerned that the excess air would build up to much positive air in the crank case. But I guess not


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## VRBehavior (Dec 29, 2006)

You guys are ****ing awesome. I think I have my answer.


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## The1Bill (Dec 8, 2009)

Nope, your better off without a spacer. At most, get a DV+ from GFB. You probably won't need it, though.

Sent from my XT1096 using Tapatalk


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## kbad (May 26, 2007)

VRBehavior said:


> You guys are ****ing awesome. I think I have my answer.


anytime, mate ... i've learned a lot about my vw's on the vortex - kudos with utmost gratitude and respect to each and every one who takes the time to contribute and share their experience, knowledge and mistakes - there are many lessons to be learned, specially from the seasoned power modders .. good luck .. enjoy the ride!


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## WILLCCU (Oct 26, 2015)

OK...thanks for that education and let's move to another area...what about aftermarket charge pipes which eliminate the neck-down area of the OEM part? Is there some power with an aftermarket unit? If so, when" 
Thanks!


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## snobrdrdan (Sep 10, 2008)

VRBehavior said:


> So increased power levels aren't an issue for the DV?


Assuming you have the newer/piston version, this should answer your question:
http://www.golfmk6.com/forums/showpost.php?p=2410906&postcount=223


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## The1Bill (Dec 8, 2009)

WILLCCU said:


> OK...thanks for that education and let's move to another area...what about aftermarket charge pipes which eliminate the neck-down area of the OEM part? Is there some power with an aftermarket unit? If so, when"
> Thanks!


I've heard anecdotes that eliminating the pancake pipe on the turbo discharge will help the turbo breathe at higher RPMs. I've done both pipes and can feel a difference, I didn't see any acceleration difference between 40-60 or 60-80 with the Torque app or Pillar FIS. That is to say that the improvement could have been to throttle response or something, but the acceleration improvement within those intervals with a stock turbo was < 0.1 second (the resolution of my tools).

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## VirgoPHD (Dec 12, 2014)

The1Bill said:


> I've heard anecdotes that eliminating the pancake pipe on the turbo discharge will help the turbo breathe at higher RPMs. I've done both pipes and can feel a difference, I didn't see any acceleration difference between 40-60 or 60-80 with the Torque app or Pillar FIS. That is to say that the improvement could have been to throttle response or something, but the acceleration improvement within those intervals with a stock turbo was < 0.1 second (the resolution of my tools).
> 
> Sent from my XT1096 using Tapatalk


I just installed my turbo muffler delete kit over the weekend and pretty much share the same opinion. I think they only real game changers for HP and torque, are Turbo and intercoolers plus tune. I can't believe I thought the spacer was helping to protect me from the common seal issue.


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## The1Bill (Dec 8, 2009)

VirgoPHD said:


> I just installed my turbo muffler delete kit over the weekend and pretty much share the same opinion. I think they only real game changers for HP and torque, are Turbo and intercoolers plus tune. I can't believe I thought the spacer was helping to protect me from the common seal issue.


I think that with a bigger turbo, the TOP and throttle body pipe will make a difference. I also think that there's more to be had with an charge air cooler ("intercooler"), as I can see my IAT working its way up during my commute without really pushing it. That bit that is left to be had won't be on the first run of the day, mind you. It would just let you go longer before losing the performance you already have.

Maybe this is the season I'll replace the cooler. So many ideas, so little time.


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## WILLCCU (Oct 26, 2015)

The1Bill....can you explain that a little better? And what is IAT? 
Thanks! New to these turbo's


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## The1Bill (Dec 8, 2009)

WILLCCU said:


> The1Bill....can you explain that a little better? And what is IAT?
> Thanks! New to these turbo's


Certainly. IAT is the intake air temperature as measured after the charge air cooler.

That cooler's job is to return the intake air to as close to ambient as possible. When getting on the throttle, the difference between ambient (outside) air temperature and IAT increases, which is to be expected - the turbo is compressing the air and heating it in the process. What I have noticed, however, is that takes the stock cooler a long time for the IAT to go back to where it was after I've had my fun.

In other words, there is a cumulative effect with the stock cooler. A well designed larger cooler would suffer far less from this; it would more efficiently cool the charge air (more surface area for the "cool" air passing by the cooler to pull heat out) , and it would be physically heavier (which will allow it to absorb more heat rather than passing it into the engine).

I'm not crazy about the stock intercooler location, either, being sandwiched between the radiator (~100°C) and the AC condenser (I don't even know what temperatures this will reach).

If I missed or glossed over something important, let me know. I'm chock full of mostly useless knowledge.  

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## kbad (May 26, 2007)

The1Bill said:


> ... I'll replace the cooler...


Ditto the1Bill .. Inter cooler design and effectiveness are key in a turbo system .. That 'temp difference' is what you're trying to minimize .. A well designed ic will flow the charged air without causing it to big down and lose its effectiveness .. The simplest oem solution is to swap the ic with one from a Golf r or Audi s3 .. They both flow much better - the r one has a newer internal design .. Good luck!


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## The1Bill (Dec 8, 2009)

kbad said:


> Ditto the1Bill .. Inter cooler design and effectiveness are key in a turbo system .. That 'temp difference' is what you're trying to minimize .. A well designed ic will flow the charged air without causing it to big down and lose its effectiveness .. The simplest oem solution is to swap the ic with one from a Golf r or Audi s3 .. They both flow much better - the r one has a newer internal design .. Good luck!


Well, at least I don't have the Texas heat with which to cope. In New England, flow can come second to size as a big intercooler can be a great heat sink.

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## WILLCCU (Oct 26, 2015)

Thanks...I get the temps of the intercooler and all, just didn't know what IAT was. How are you getting that data? 
I live in sunny Arizona and hot weather is just around the corner! Stage II software is supposed to be here mid-week next week. There was delay due to my 6-speed manual transmission. HPA is the source. 
I'm thinking IC will be next level before I step up to K04 or better. But that would be awhile off. Still under warranty (only 10,000 miles on the CC). 
Is the Golf R / A3 still sandwiched? What's the best advice for aftermarket? Snow Performance?


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## The1Bill (Dec 8, 2009)

WILLCCU said:


> Thanks...I get the temps of the intercooler and all, just didn't know what IAT was. How are you getting that data?
> I live in sunny Arizona and hot weather is just around the corner! Stage II software is supposed to be here mid-week next week. There was delay due to my 6-speed manual transmission. HPA is the source.
> I'm thinking IC will be next level before I step up to K04 or better. But that would be awhile off. Still under warranty (only 10,000 miles on the CC).
> Is the Golf R / A3 still sandwiched? What's the best advice for aftermarket? Snow Performance?


Well, I have a few options. I have a P3 that can grab temperatures and show them on my vent gauge, a Polar FIS that will put parameters in my MFI in the gauge cluster, a Bluetooth single and the Torque app for when I want to log, and VCDS for when I want to log with a laptop. Torque logs are my usual days source, though. 

To my knowledge, all OE VW charge coolers are sandwiched. To get away from a sandwiched cooler, you'd need something like the Neuspeed FMIC. I think that I'll stick with a sandwiched cooler, though I'm having trouble deciding which one. The R aftercooler looks perfect for my needs, though.



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## VirgoPHD (Dec 12, 2014)

I have the P3 VIDI gauge in my CC too. The sandwich intercoolers are too
Expensive when you consider that from mounts work just as good if not better. So I think I'm going FMIC. But since I went stage two I realize now I need a stiffer suspension the car rolls way more now than before


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## VirgoPHD (Dec 12, 2014)

The VIDI gauge though was well worth the money I get my codes on instant and all my readings, now that I think about it I have to order the analog adapter


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## The1Bill (Dec 8, 2009)

VirgoPHD said:


> The VIDI gauge though was well worth the money I get my codes on instant and all my readings, now that I think about it I have to order the analog adapter
> 
> 
> Sent from my iPhone using Tapatalk


I found mine in a junkyard, actually. I was looking through car-part.com, and one of the listings had pictures. In one of those pictures, I saw the P3 in the gauge. $100 and three days later, I had the P3 VIDI with the analogy sensor in my hand.

It's a neat tool, though I still like my other gauge and logging tools too.

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## VirgoPHD (Dec 12, 2014)

The1Bill said:


> I found mine in a junkyard, actually. I was looking through car-part.com, and one of the listings had pictures. In one of those pictures, I saw the P3 in the gauge. $100 and three days later, I had the P3 VIDI with the analogy sensor in my hand.
> 
> It's a neat tool, though I still like my other gauge and logging tools too.
> 
> Sent from my XT1096 using Tapatalk


I am envious


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