The air filter box on my '93 Rx-7 has two small lines coming out of the back of it. Both have similar looking vacuum actuated valves. Can someone tell me what they do and how they should behave. I noticed when I changed the air filter that the upper one seems to be open and on another Rx I checked, it is closed (cars not running, no vacuum applied).

I'm trying to figure out why my new Pettit turbos don't seem to perform and wonder what connection, if any, these valves may have.

 

Uhhhh ... you mean the factory blow-off (BOV) and factory pop-off valves (POV)? I'm taking a stab here because I haven't looked at a stock engine bay in years.

To put it short and sweet because you could easily search for this, a BOV releases compressed air buildup when the TB is suddenly closed to keep the turbos from being suddenly choked (therefore keeping them spooled for easier boosting in the next gear ... or just from excess wear when you stop). The POV is a safety device that is designed to release pressure if the boost were to spike beyond a certain threshold with the idea of not allowing that excess boost to reach your engine ... though I'm not sure what the factory one is made to pop at (it's gotta be mid-upper teens psi, I would think).

What do you mean by "open"? Venting into the atmosphere?

 

By "open", I meant that with the car not running (and cold), I could blow into the upper hose with no restriction. I could not do that with the bottom hose. Hence the upper valve seemed to be open.

However, yesterday I went to see my car and retried the blow test on both hoses and the upper one was closed. Perhaps the valve in the upper hose, whichever it is, is sometimes sticking open. Since I have just had new Pettit turbos installed, and they don't seem to work worth a darn, I was trying anything I could think of and figured, why not give them a blow ... My mouth got a little dirty but I may have learned something, although I'm not sure if its relevant to my dismal performance.

From your description, it sounds like the BOV or POV (don't know which is which, only that the one in the upper hose is the sometimes open one) could be letting my air escape out the wrong end (so to speak) of the piping system?

From your reply, I learned something else too. The tech at the shop that installed the turbos, said the open valve was part of the pollution control system! Luckily, I have moved the car to another shop. Unfortunately, it now appears (after two, or is it three weeks) that this other shop doesn't have much of a clue either.