Today kids, we are going to talk about blow off valves. Mmmkay? Now, we know there is a lot of good information out there in regards to BOVs and other types of valves. However we like pictures, because they are good. Let’s start with the basics, a blow off valve is a type of valve used to regulate air pressure or boost from a turbo system. It is like a diverter valve in that they both work to regulate pressure. Both DVs and BOVs do the same thing, the difference between the two is in the way they work. A diverter valve takes excess boost and dumps it back into the air box or intake, making the turbo a closed loop system. A BOV takes that same excess boost and dumps it outside, making it an open loop system. The reason for both types of valves? Simple, a turbo spins between 100 thousand and 200 thousand RPMs, creating a large amount of air pressure or boost. When the throttle body is shut rapidly after that boost is created it needs some where to go. If the pressure is not released, it blows back into the turbo and stalls the veins. 100 thousand rpm to zero in a few seconds is probably not the best thing for your turbo.
Now let’s talk about specifics, Audi engines are for the most part designed to use diverter valves, not blow off valves. This is based on the way both valves work, DVs send the boost pressure back into the system, leaving no drop in boost. BOVs on the other hand, bleed off the pressure and require a recirculation kit. In a stock engine, a BOV can rob boost and possibly stall the engine. Now this doesn’t happen every time, but when it does, you can find yourself in a world of pain. Of course you can go MAFless, meaning you can run a BOV without these risks. However there are problems and risks with that route as well. So if you do decide to run a BOV, make sure your engine has the components to make up the loss in boost and do your homework. Know what risks you are taking with unmetered air. Also important to note, is the fact that removing the MAF for better airflow is really only needed for big builds. The sort where whole engines are changing, and in that case, the rules change as well. To be clear, CleanAudi recommends running a DV, not a BOV or any combo either. DVs are much safer because they work with the pre-existing engineering. Not to mention, that DVs create no boost loss, meaning the highest level of performance. So BOVs are really just for a pretty noise, and rob the car of performance. (We are pretty sure that tuning for pretty noises qualifies for rice status) Now if you really need that swoosh sound, a diverter valve with a cold air intake will produce the same effect. So the moral of the story is simple, use a damn DV, and forgo the BOVs. They don’t work with Audi engines, unless you have built the engine to work with one. (AKA MAFless) As for a brand for DVs and BOVs, you get what you pay for, so stick to the good stuff. We recommend Forge, the 007 DV is great for those 1.8ts out there. As for BOVs go with Tial. Period. As always happy wrenching and build it right, not twice.
Here is the sound we were talking about earlier: