Even though blow off valves (BOVs) are all the rage, it is important to remember that you do not gain horsepower with a BOV.

The BOV does, however, affect throttle response, saves your turbo from back pressure, and reduces turbo spool-up in between shifts.

Furthmore, if you plan on making more than 17-18 psi boost...You should replace the stock blow off valve.

Now there is a lot of debate of what kind of BOV to get. There are basically 3 kinds:

• BOVs that vent to the atmosphere
• BOVs that vent back to the Intake (pre turbo)
• Hybrid BOVs that vent to both the intake and atmosphere (some are even adjustable).

Venting to atmosphere is fine most of the time...and that is what that cool, loud popping sound between gear shifts you hear in the WRC cars.

However, the factory BOV vents back to the intake and accounts for the air in the intake when it sets air/fuel ratios between shifts. At its worst, your car will temporarily run rich between shifts and could even hesitate/stall. For most vehicles and various stages of engine management, however, this is not a significant issue (most people never even notice anything).

In order to avoid any potential air/fuel issues it may be preferrable to get a high performance BOV that either vents solely to the intake or a HYBRID that vents to both.

A HYBRID really gives you the best of both worlds...especially the adjustable ones like the GFB Stealth. You determine the volume of sound by choosing how much to vent to atmosphere