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Diverter valve vs Blow-off valve on a 1.8T

128K views 49 replies 23 participants last post by  boosted_starion 
#1 ·
ok, so this is for the many questions regarding the use of a dv vs bov on your turbo vw motors.

First off, what does the DV do?

When you hit the gas your throttle plate opens allowing air into the engine. The turbo is in the intake stream and compresses the air and forces it in to the engine at a certain pressure. When you need to shift and let off the throttle, throttle plate closes, and the turbo is still spinning. The turbo still spinning is a good thing because it will have less work to catch back up when you reapply the throttle, but... a spinning turbo means it is still compressing air and the throttle plate is closed so there is only one way for the compressed air to get out, back the way it came in. Well this is where the Diverter Valve comes into play. The diverter valve diverts the air that would have gone back through the turbo causing it to stop spinning in one direction and spin backwards, to go back into the intake stream pre-turbo so you recycle that air. Now since your Volkswagen is tuned to run the air back into the system after the MAF sensor the MAF is calculating based on a certain charge still being in circulation when the throttle plate re-opens. This is why using a DV is most efficent on vw's motors, rather then a BOV which vents to the atmosphere. If you were to put an aftermarket Blow-Off Valve on the system that air that is being calculated for just blew out into the atmosphere. This causes the computer to still inject fuel metered for the air that was in the system already as well as the new air coming through the intake. With an aftermarket blow off valve you will get a fun turbo sound but your engine will run a little richer. So basically you need to pick performance or sound?

Benefits of an aftermarket DV:

Your stock valve in your car regulates your turbo power. At idle, your valve is open from vacuum pressure. When you hit the throttle, the diverter valve begins to close. When fully closed, turbo boost is allowed to be delivered to your engine. When you lift the throttle, the boost pressure is released from the valve into your air cleaner box. Inadequate/defective valves have extended lag, loss of boost, sluggish throttle response. A aftermarket diverter valve can clear up the previously mentioned problems. Also, if you have a chip, you need an aftermarket valve now. Chips simply kill stock diverter valves.

Stock oem DV:



Here's a common upgrade for an aftermarket DV, Forge DV:



here's a solution if you want both performance and sound with your 1.8T motor. It's called the splitter by forge, it does both recirculate to keep the performance, but it also vents some air to the atmosphere, thus actin like a normal BOV.



Here's some common BOV's *i dont recommend, but its your car*

HKS:



Forge:



Also here's another performance upgrade you can do with your DV. It's a relocation kit. By relocating the valve in this way there are two benefits. Firstly, due to operating in lower temperatures the longevity of the valve is increased. Secondly, after relocation, the air that is recirculated back into the intake tract to the turbo will be cooler. Cooler air has a greater density. The greater the density of the charge mix in the cylinder the more power generated on combustion. Here's a kit from forge.

Forge Relocation Kit:



Now, all of these products can be found at normal vw's parts stores online. Hopefully this helps some questions about DV's vs BOV's.
 
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#5 ·
if u have a stock dv, id say to upgrade to another dv, like forge or apr. if u have a bov, yes, switch it to a dv for better performance. vw's need the recirculation to run properly, if u want the splitter is the best way to go for bov sound and dv performance still. u can adjust how much recirculates and how much vents to the atomsphere.
 
#8 ·
Lose power and run rich...

In short, the MAF sensor calculates the amount of air entering your system, which is placed before the turbocharger. The turbo compresses that air, and when you let off the throttle, the pressurized air in the system has to go somewhere, right? Well if you shoot it off into the atmosphere, that's a bunch of air lost that the car thinks is going into the intake. If the car thinks that air is there, its gonna send fuel to go with it... And thats how you end up running rich, thus losing performance too.
 
#10 ·
Not exactly sure what a good DV is for you since you have the MKV with an electronically actuated diverter valve. I'm sure APR makes one, as well as Forge. Both are great companies, so check into them. However, diverter valves/blow off valves will never have an impact on horsepower/torque, as well as fuel mileage. The BOV noise your looking for has more to do with your intake system than with the valve. A short ram intake, dual intake, or even a modified airbox with a higher flow pannel filter will result in a decent amount of sound.
 
#11 ·
So apparently hks makes a BOV that closes at idle, making it okay to run on a 1.8t? Saw it on YouTube. Anybody heard of this? Looking into some stuff for the bf since he's gonna buy a GLI.
 
#12 ·
lol wtf? BOV's will just never work. Air exiting to the atmosphere instead of into the intake = rich conditions. There's no way to get around that unless you get one of those ''hybrid valves'' which does a little of both (Vent and recirculate).. And aparently the 1.8Ts don't mind it.
 
#15 ·
I watched a couple minutes of that and they guys argument doesn't make any sense. I mean wtf they put a bov on a NA car... and a bike...

They are saying that BOV and DV will make the same power. Which is true, but that doesn't mean they will both work properly. The reason BOV's are bad is because when you left of the gas they vent all the air to the atmosphere. That's bad because the car is expecting it to be there and its not which cause your car to run lean and takes longer to build boost after shifting. HKS's don't cause as much of a problem's because they are closed at idle, but they still vent to the atmosphere like other BOV's.
If you get the HKS and get the recirculation adapter.
 
#16 ·
I watched a couple minutes of that and they guys argument doesn't make any sense. I mean wtf they put a bov on a NA car... and a bike...

They are saying that BOV and DV will make the same power. Which is true, but that doesn't mean they will both work properly. The reason BOV's are bad is because when you left of the gas they vent all the air to the atmosphere. That's bad because the car is expecting it to be there and its not which cause your car to run lean and takes longer to build boost after shifting. HKS's don't cause as much of a problem's because they are closed at idle, but they still vent to the atmosphere like other BOV's.
If you get the HKS and get the recirculation adapter.
Thanks for the info!
 
#20 ·
So I have a question, if I go with the Forge Splitter Valve is it also possible install it with the relocation kit? Im wanting to put an aftermarket DV on, but i want the BOV sound. After reading this thread I'm convinced to go with a DV. So why not go with the best of both? I'm liking the benefits of the relocation kit too, thats why i ask.
 
#22 ·
I don't see why not, there's not going to be any hoses for the BOV port just the DV port so there's not reason you cant use it with the relocation kit. Just remember the forge splitter gets installed upside down compared to a regular DV so just make sure you hook it up right or else you'll have a vaccuum (spelling..) leak.

is there any maintenance for the forge splitter?
The forge splitter is a piston type valve so yes it will require maintenence every 5k miles or so. Same as any piston type valve, DV or BOV. It's only the diaphram type valves that don't require maintenence and maybe a select few valves say that they don't require lubing.
 
#28 ·
No. Custom turbo setups use mafless intakes. Meaning they use readings from an A/F gauge to custom tune the fueling to match the air flow (that's the proper way to do it, guys that just slap on MBCs are stupid). Our cars use a maf that comes before the DV. Our computer automatically calculates how much fuel to use based on the maf readings. The air going through the DV is precalculated so if you remove the DV you're taking air away that the car thinks is there and since its air that goes in after the maf the car has no way of knowing that its not being put in.

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#33 ·
You can buy a kit to relocate the valve to the cold side of your turbo but idk about more efficient. The turbo is hot as hell already and its not being combusted until after it hits the IC. All it really comes down too is bov=wasted air and dv=reused air. A good way to look at it is If you could have a cat that filtered the extra fuel and put it back in your tank would you take it out for a cat that just burnt it up and spit it out?

Sent from my Phablet AKA Samsung Galaxy Note 4G LTE via the dark side.
 
#35 ·
When you let off the gas the boost pressure has to go somewhere so it doesn't hurt the turbo. A BOV blows it off into the atmosphere. Once the air gets blown off its gone, it doesn't help nor hinder your engine in anyway. A dv blows it back into the intake. It recycles the pressure which actually helps your Turbo spool up faster than it would if you had a bov. Maybe not a huge noticeable difference but still a difference. Even if you tune your car for a bov all its doing is taking away the extra fuel you cpu pre calculates for the dv so you don't run rich. But you're still losing the efficiency of reusing the pressure already built up from the previous gear.

Sent from my Phablet AKA Samsung Galaxy Note 4G LTE via the dark side.
 
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