Blow off valve
 

Where in an 93 rx7 is the blow off valve located

Looking at the stock air box, the top hose that is about 1.25" in diameter has a valve on it with a single long vacuum hose that attaches to the intake plenium. That's the blow-off valve.

It's attached to a hose that's plugged into the stock airbox. If you're looking at the back of the airbox, you'll see two smaller hoses in a over/under arrangement, and the lower one is what the stock BOV is attached to (there's a small section of hose between the BOV and the airbox).