Hess Sport

what is the"hess" sound when ppl release the gas padel on sport car ??

what is the"hess" sound when ppl release the gas padel on sport car ?? did ppl mod their car or does it come with it from the manufacturer?

the loud "hiss" or "pssh" sound when the pedal is released is caused by released excess or back pressure also known as "boost" from a turbo (turbine) . The excess boost is let out through something called a blow off valve (BOV) which vents into the atmosphere, or a Bypass Valve (BPV) which vents it back into the air intake system.

The purpose of this is to prevent "overboosting" and "boost surge". A turbo uses PSI (pounds per square inch) to force more air into the engine (forced induction) by using the exhuast gas routing through the turbo housing ie the more exhaust (higher rpm) the more boost (power).

Over boosting is exactly like it sounds, if an engine is set up to handle let's say 15 PSI of boost, the BOV can be set to 15PSI and will vent anything over that when it reaches to prevent damage to the enigine.

The main reson for a BOV or BPV though is to prevent boost surge. In short and simple Boost surge is when the air being forced into the engine through the piping actually comes back through when the pedal is released, if a valve is not used to vent it before it reaches back to the turbo you risk bending the fins inside it, or possibly detonating it all together.

Valves also come in a variety of different sounds depending on the company, the stock BPV on my mr2 sounds like a rattle snake, others just make a really lound "psssh" sound, and even one that sounds kinda like a seal. Either way when you hear a sound like a lot of air going through a small hole it's probably a turbo.

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