2010-05-03 Calgary Audi S4 Forge Motorsport Bov
There is a lot of politics behind blow off valves. Mostly stemming from ricer Honda's and Skylines who rev their engine to make the sound.
There are many benefits to a properly tuned blow off valve or splitter. When the turbo builds pressure in the piping between itself and the engine and the throttle plate suddenly closes... The pressure continues to build from the momentum of the turbine. That pressure needs somewhere to go, so it tries back out throuth the turbo. This backwards flow of pressure puts pressure on the turbine shaft and also slows the rotation. This means shorter turbo life and less performance.
The BOV will open to release the pressure when the throttle plate is closed due to vacuum. The problem with releasing all of the pressure causes poor performance because the turbo must now rebuild that pressure. So tuning the BOV with a proper spring rate for your maximum PSI is important!
Additionally, if your tuning system uses a MAF (Mass Air Flow Sensor), the computer will have already measured the incoming air that was exhausted out of the BOV. This causes a very rich condition between shifts as the BOV vents.
To prevent rich conditions from a MAF system, adjustable Splitter BOV's allow you to configure how much air is released into atmosphere, and how much is put back into the intake (Before the turbo).
Auto manufacturers favour a full recirculating valve due to noise concerns, but that causes less performance. By venting a percentage of air into the atmosphere causes a siphoning effect, also called scavenging.
I purchased two Forge Motorsport Splitter Blow Off Valves for my Audi S4, and these are them.
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