Pre-95 BOV FAQ

      Replacing the stock Blow Off Valve (BOV)/Compressor Bypass Valve (CBV) with a better one is really a no brainer . . . once you've done it.  To be honest there really is no need to have a BOV FAQ, however like myself, many new members to Club DSM are nervous about doing mods without getting a handle on what is involved. With this in mind I have decided to write this FAQ so that you newbies can get a feel for what is involved, and to point out a few of the minor yet annoying things that can go wrong and cause you to curse the day you ever thought about modding your car.

Parts (some may not apply depending on you upper IC pipe and BOV):

Tools:

OK from here on I'm going to assume you have the stock upper IC pipe and are going to be installing a pre-95 BOV which you purchased from one of our favorite DSM vendors with an adapter.  Now a few notes about the adapter.  I bought my BOV used from another 2g owner.  Based on my experience with this one (and comments from other 97 owners) this adapter works fine on the 95 and 96 models but on my 97 the inlet of the BOV was too small even with the stock rubber boot.  The result was that it would keep popping out under boost.  I tried RTV, but that didn't hold.  What I finally did was to use the wire ties I mentioned in the parts section to hold the BOV in.  The seal was fine but there just wasn't enough clamping force to hold the BOV on.  I spoke to the Dave Buschur (who made my adapter) and to the guys from Archer Racing at the shootout about my problem.  They said they knew about it and were working on it.  All that is required is to increase the size of the inlet and maybe add a bead to the end so I'm sure they have it taken care of by now.  But make sure you ask about it so you don't have to find out what fuel cut feels like when your BOV pops out under boost on the highway (Tip: always bring your tools with you on your test drives).

Now if you have a after market Upper IC Pipe (and a pre-95 BOV) which doesn't require an adapter then the only thing you really need to worry about is getting a good seal between the base of the BOV and your mounting flange. Just make sure you get a good seal or you'll just be venting your boost to atmosphere. Not only does this sound bad, but it will also screw up how the engine runs since air that has been "counted" by the MAS will be purged from the system.

As for other aftermarket BOVs like the HKS sequential, I don't know much about them except they cost more and sound cool.  I am assuming that you can put one on a stock Upper IC Pipe as long as you buy an adapter.  Please correct me if I'm wrong.  Incidentally DmTalon heard my car and thought it sounded like really nice and thought I was venting to atmosphere.  I'm not bragging, the point is that a 2g with a pre-95 BOV, and K&N 3000GT FIPK sounds very nice, loud, and trick.  So don't think that only the aftermarket BOV's sound cool.  If you want the ability to adjust your BOV then obviously the aftermarkets are the way to go.  Otherwise go for the pre-95 BOV  . . . they are much cheaper.

OK, so how do I do it you ask.

To start here is a picture of the stock BOV, pre-95 BOV and a rubber boot I'll discuss later. Notice that the vacuum port sticking out of the pre-95 BOV (left) is rotated 90 degrees from the where is it on the stock BOV (right). Notice the boot at the bottom of the picture, and the fact that the pre-95 BOV adapter doesn't have a ridge on the bottom tube which goes into the upper IC pipe.
First thing you'll need to do is remove your stock BOV:
  • Remove the hose running from the top of the BOV to the throttle body
  • Loosen the clamp holding the base of the BOV to the Upper IC Pipe
  • Loosen the clamp holding the BOV outlet and return hose together. 
  • Now slip the BOV out and set it aside.  You'll notice a rubber boot around the base of the stock BOV.  Remove this and save it.  You'll need it in the next step.

Now all you need to do is put your new BOV on.  Remember that rubber boot I told you to save; well put it on the new BOV. (Don't tighten any of the clamps yet):
  • Insert the BOV into the Upper IC Pipe but don't tighten the clamp yet.
  • Connect the hose connecting the BOV outlet to the return hose.  Don't forget the clamp :)
  • Connect the vacuum line from the throttle body to the port at the top of the BOV
  • As mentioned earlier, the vacuum port is angled differently than the stock one.  This is OK and you should be able to pull the hose that connects to it to make it reach.  Make sure that you don't cause it to kink or wise you'll have problems.

Now tighten all the clamps and check your connections.  The BOV might feel like it will pop out under boost. Guess what, it will. To solve this problem I wrapped wire ties (not shown) around the BOV and the upper IC pipe. I placed the ties between the bolts holding the adapter to the BOV and the body of the BOV. The picture above shows how I put the ties on with a red line. There is no need to tighten them down a lot.  In fact I only used one and it is holding perfectly. The point is not to squeeze the BOV down, but to prevent it from sliding up. So, just a little but if tension on the ties will do the job. In fact I only used one (in the location noted above) and it is holding fine, however, two will be even safer.

Go test drive the car and make sure everything passes the sanity check (i.e. proper sounds, boost levels, spool up after shift, yadda yadda yadda).  Don't forget to bring your tools with you just in case it pops.  When mine did (it didn't happen until I was mile away) I had to drive home with no more than 1/8th throttle and no more than about 20 mph or I would get fuel cut.  Interestingly enough the stock gauge was reading max boost :)  I'll assume though that you already have a true boost gauge . . . RIIIIGHT!!!!

Enjoy.