911, 911 Porsche, Audi, Porsche, porsche performance, turbo Porsche, VW

Stock vs. Billet Diverter Valves

This topic came up on a couple of forums earlier in the year, so I wanted to share a bit of knowledge with you guys. You see a lot of posts recommending billet diverter valves on the market which are replacements for the stock units. We sell and install many of these billet valves to combat the boost issues we see from a failed stock valve. This is one of the first things we recommend doing to the car, especially if you are thinking of flashing your ECU to higher horsepower levels. Why does this matter? What makes them better than the stock units?

Here’s why: The stock units contain a rubber diaphragm in them that over time will tear, causing the valve to not function properly. Porsche, VW, and Audi have been using these Bosch valves in their turbo charged cars since the early 80’s, and still are using them today. Sure they use an “updated” valve, but it fails in exactly the same manner as the old valves (as well as looking the same). Typically we see these valves fail by 30k miles. In cars that run higher boost levels, the Bosch valves will fail almost immediately, because the rubber diaphragm is not designed to resist the increased pressure. It will rip and fail, and all of a sudden that $2k ECU flash that you just paid for, will seem like you got ripped off (I.E. the car will produce less boost than stock).

What are the symptoms of a failed valve? Typically you will only be able to boost a fraction of what your car should. For example, if you are normally running 1 bar of boost with a good valve, well then with a ripped valve you may only be able to produce .4 bar. This is a significant decrease in horsepower.

Here is a picture of a stock Bosch valve that I cut open and pulled apart. The red arrow points to the rubber diaphragm which will split and cause the vacuum leak. What happens, is the air is not able to push the plunger up, because it travels right through the rip. If the rip is small enough, well then a lot of air will still partially be able to push the plunger up, which is where you might still get your .4bar of boost. Basically it is like trying to blow up a balloon that has a tiny hole in it. You might be able to blow it up a little bit, but you won’t get it all the way. In the case of the DV valve, it is vacuum, but the theory of air movement is the same.

Bosch Valve

And here is a picture of the Billet Diverter Valve we use. Notice the aluminum plunger, which is sealed tightly by the rubber o-rings on the side, eliminating the need for a rubber diaphragm. This virtually eliminates the valve failure. And since I know it will be asked, “Can the o-rings fail?” In theory yes, they could. In the last 2 years, I have had 1 valve come back with a bad o-ring, and this was a new valve, so I contribute that to a manufacturing defect. In contrast, last week alone, I removed 5 Bosch diverter valves that were shot from vehicles. A drastic improvement! With a billet valve, you will also be able to run higher boost levels without fear of failure. We recommend them with all of our ECU flashes, as the boost is increased over stock levels. Replace the stock valves with billet units, and don’t worry about them again

Billet Valve


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