A diverter valve is a valve set in place to protect the turbo charger from compressor surge. When you let your foot off the gas, there is a large amount of compressed air that needs to go somewhere. The diverter valve allows this compressed air a way out. If this air had no where to go, it would try and force it's way backwards through the turbo, causing negative effects, anywhere from just slowing the turbo down unnecessarily to complete turbo failure. This is not good. So the diverter valve/blow off valve/bypass valve/dump valve was invented. All these valves function in the same manner, allowing this excess compressed air to exit the normal path of charged air. The biggest difference, is that a blow off valve is intended to allow air to be released straight into the atmosphere. This is the action resulting in the Fast and Furious sounds many people love and expect from a turbo engine. A diverter valve reroutes the charged air back into the inlet of the turbo to be run through the engine all over again.
Here is the basic operation of a bypass valve:
When the throttle plate is open, the air pressure on both sides of the piston in the blow-off valve is equal and the spring keeps the piston down.
When the throttle is closed, a vacuum forms in the manifold. This in combination with the pressurized air from the turbocharger moves the piston in the valve up, releasing the pressure into the inlet of the turbo (Recirc.) or the atmosphere (BOV).
As seen in the diagrams above, which is the most common way a diverter valve operates, the piston is actuated by intake manifold pressure. The OEM diverter valve for the 2.0tfsi engine works in a completely different manner. The OEM DV is actuated by an electromagnetic solenoid. instead of manifold pressure, the solenoid is actuated by an electronic signal from the ECU. This is a faster and more accurate manner of actuating the dv, meaning that the DV can be actuated the same moment you take your foot off the gas, rather than waiting until the manifold pressure in the engine drops to actuate the DV. In my opinion, this electronic actuation is a superior method to any vacuum operated DV.
So now that we have that out of the way, lets go over the OEM DV options that came with the 2.0tfsi. There are two major variants of the OEM DV. Revision G and Revision D. Revision G is the original style that came standard on 05.5-06 model years of our A4. It consists of a plastic piston with a rubber diaphragm.
In my opinion, this version of the DV actually outperforms the newer revision DV. BUT, it is highly unreliable. The rubber diaphragm can easily form a tear and you will lose boost. This is very, very, very common. You may never even notice this on a stock car, as the boost is low. But once you increase boost to 18-20 psi, you will notice immediately when this valve fails. I have run this version valve on my car for roughly 15-20k miles, and went through 3 of them.
Here is the tear on my most recent failed Revision G DV:
This dropped me from normal 20ish psi operation down to about 12 psi in one drive home. It can fail for absolutely no reason, and will leave you with very little performance. Again, it can be torn already in a non-tuned car, and you may not notice, but the turbo is definitely being over worked to make up for this loss of pressure. And the second you tune your car, you will know something is wrong.
Lets move on to the newer Revision D DV that comes standard on most 07-08 A4s.
All rubber parts have been replaced by solid plastic, allowing for a more durable part. Unfortunately, this also keeps the valve from creating a strong seal, since there is no rubber surface on the end of the piston to create a strong seal like on the earlier Revision G model. The unfortunate thing about this revision, is that most people see it as the be all end all of diverter valves for our car. When in actuality, this dv performs worse overall than the original DV, although it rarely fails. But from what I have read, it is actually designed to leak pressure. In my own experience, using this revision DV provided slower response, slightly lower peak boost, and less reliable operation. Peak boost always varied from run to run, and performance was better and worse on different runs for no apparent reason. I believe this revision DV is actually the worst option available, although it is the only acceptable OEM DV, as you never have you replace it.
I am not even going to go over any blow off valve, or BOV spacer info in this thread. As our cars use metered air, and if you use a BOV or spacer, you are allowing this metered air to leave the engine, and the engine in turn will run rich any and every time the charge air is released to atmosphere. The only way that this is a feasible option for our car is to do a MAF relocation, and this is not the thread to go over this option.
So then. What do you do if you want better, more reliable performance out of a diverter valve? You must go aftermarket. So what are your options?
Turbosmart - ~$225
Forge - ~$200
AWE - ~$130
These are the only 3 aftermarket DVs that I could find that are specifically made for our cars. The biggest problem with any of these aftermarket options, is that they ditch the electronic actuation completely, and rely solely on manifold pressure to work the DV. This not only allows for slightly slower response, but also requires installing a boost tap, and running a vacuum line across the engine bay.
The Forge is the most widely known and used. It is a complete system, and you can actually buy different strength internal springs to allow for different boost applications. You probably shouldn't mess with these options on stock turbo, as it would be very easy to create an overboost issue, and go into limp mode. I have never heard a confirmed report of a failed Forge on our platform, though they do require maintenance from time to time to ensure trouble free operation. You will need to open it up, make sure the spring is seated correctly, and oil as needed. I have not personally run this DV, but have helped install one, and the DV is solid in build, and is a good quality reliable product.
The Turbosmart option is a very similar product, though I was unable to dig up much information on it. It is slightly more money than the Forge, though I consider both to be more expensive than necessary.
The AWE dv is basically a reworked version of an OEM Porsche DV. It is the cheapest of all above options, and has been tested up to 750 HP applications. Though I don't believe I've ever heard 1st hand experience of anyone using one.
Though these are the only options made specifically for out platform to replace the OEM DV, you still have other options available to you. Keep in mind, any other DV that is not specifically built for the 2.0tfsi, will most likely need a DV relocation kit. Probably the most popular DV of this type, is the Synapse Synchronic DV. It costs ~$200 by itself, plus what ever it will cost you to relocate the DV and actually be able to install it. From what I have read, this DV is supposed to be superior to the other DVs on the market because of it's response time. But the work required to install, and the cost, far out weigh it's pros for me. Also, it still relies on vacuum pressure to actuate it, so no matter how fast it is, it still can't be as fast as an electronically actuate DV like the OEM version.
So what is a girl to do?
There has been a recent breakthrough by an Australian company Go Fast Bits. They have come up with (IMO) the ultimate solution. What they have done is made a rebuild kit that installs onto the OEM electromagnetic solenoid. This way it retains the electronic actuation, but also upgrades all working parts to metal components. This was the ultimate choice for myself, and is what I have gone with myself. The build quality is superb, and the engineering behind it is amazing.
It replaces all moving parts from the OEM DV, and doesn't matter what revision DV it is installed on. It is so well thought out, that it is the only DV option to us, that allows the DV to open partially. Whereas all other DVs mentioned above are either open or closed. The fact that this DV will allow it to only open a percentage of the way, depending on the circumstance, allows for faster throttle response when you get back on the accelerator. Also, they have built the DV+ in such a manner that the piston has a 25% more powerful closing force than it does opening force. This means that the DV will never open unless you tell it to.
It is also built with two different springs, unlike the OEM versions single spring. This allows the DV+ to operate by BOTH ECU command AND boost pressure. What this means is that if the ECU tells the DV to open, but there is no boost, it will not actually open. On the other hand, if the ECU tells the DV to open, and there is boost, the valve will only open as long as there is boost pressure keeping it open. As soon as the charge air drops, the DV will close even if the ECU is still telling it to stay open. This style of operation actually results in less turbo lag since the DV is not being opened/closed unnecessarily. So by design, the DV+ is only going to open just enough to avoid compressor surge. and it can open incrementally as well, to suit the situation, as opposed to 100% open or 0% open. They actually go so far as to state that peak boost (in stock boost application) will come on 30% quicker. This is the smartest DV I have seen, and on top of that, it is only at a cost of ~$135. You can order from Purems.com here.
Upon install of the DV+, I could immediately tell a difference over stock. Boost is much more consistent from run to run, boost feels like it comes on quicker and stronger, and even partial throttle acceleration is quicker. I am very happy with the DV+, but I leave it up to you to figure out which application works best for your needs. Hopefully this helps someone along the way. Feel free to add anything you think I missed, and thanks for reading.
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to GFB and their DV+
Originally Posted by 2kwik4u
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