Why Bosch BOV fails

Theory

  BOSCH makes a good replacement for our stock MK3 Supra turbo valve.  However some have noted a high failure rate on the BOSCH valves.  Due to the fact that the boost is being recirculated into the intake system, it can be hard to tell if there is a failure.  The part that holds the boost is not of a high quality construction, and can fail easily.  Let's have a look inside the valve.

The Guts

  Here is the inside of the BOSCH #108 valve which is supposed to be the long life upgrade for the stock valve.  You can see the brass metal piston which is only on the 108 valve.  The construction is very basic.  There is an opportunity here for a modification.  You could make the valve much stronger by taking the spring and stretching it out, then put back together.  You would simply need to seal the top cap with silicon or perhaps something stronger like liquid nails.  Let's have a closer look at the diaphragm.

The Failure

  This valve has not been in use for very long.  But look what has happened already.  The diaphragm is torn only after 16,000 miles.  This will cause some boost to leak past the diaphragm, into the intake.  This is not an extreme case, but over time the seal would be broken quite dramatically.  Symptoms of this include a funny noise under boost some have describe as a "farting" sound.  It seems possible this could be repaired with a little silicon, but would it ever be the same?

Final Thought

  The moral of the story here is to stay away from diaphragm related valves.  Eventually they will fail in some manner.  Still, others may never fail over thousands of miles.  The choice is yours.  These are not very expensive, and are still a good cheap upgrade for the stock valve.  If you notice your BOSCH is not what it used to be, take it apart!  You might be able to save it's life.  If not, it's not much for another!