Does anyone know what they do? My friend told me that all they do is create a noise everytime you shift in a turbo car, a noise of air coming out or something. Is this safe? Does it affect the engine in any way?

 

Yes this is safe.

Its simply releasing the pressure that gets built up.

 

blow off valves releases the pressure that is built up from the turbo when you release your foot from the accelerator. because the engine is no longer accelerating and no fuel is being injected into the cylinder and being combusted you do not want the "boost" that was developed just before to go into the engine. this is called boost "creep" where the pressurized air from the spooled up turbo continues to run into the cylinders. the blow off valve releases this pressurized air and that is why you hear the psssssst sound. it is completely safe for the engine.

 

The term boost creep has nothing to do with what you're describing. The correct term is for what you're trying to describe is compressor surge and in reality compressor surge usually isn't harmful to the engine but can cause rapid failure of the turbo turbine with high boost applications.

The term boost creep is used to desribe an overboost situation usually caused by the physical inability of the wastegate to bypass the turbine (misconfigured boost controll can also cause this problem). The wastegate is used to maintain target boost without overboosting and has nothing to do blow-off valve. Boost creep is a common problem with smaller VF series turbo with an internal wastegate with a free flowing exhaust.

 

It really depends on the car. Some cars, it is completely safe to blow off that air. On my car for example (vw jetta 1.8t), it is not a good idea because that air is supposed to be recirculated and is measured post where the diverter/bov sits. By releasing that air, I'd be fooling the ECU to make adjustment it doesn't need to do. Its a real bad idea if you like your catalytic converter.

 

Will it be a good idea on an STi?

 

Isn't a blow-off valve the same as a wastegate and don't all turbos have them?

 

NO...its different...BOF is right before the throttle body, hooked ON the tube. This just relieves turbo pressure between shifts. AND goes psssSSSSST!!

The wastegate is basically a flap that opens and away goes the extra boost ( as more RPM=more exhaust flow=more RPM on turbo's turbines=MORE BOOST) Some turboes have em some dont. Some are integrated and some are external

BTW - this sound is pimp. and so is givin rep points*

peace

 

thsiao, The isn't ideal on STi as the air is metered and is expected. This wouldn't do any damage to anything but there is potential for the A/F to go rich durring shifts descreasing performance. You would be hard pressed to come up with any explaination of how this condition could damage the catalytic converter as fast-tl suggested. The car might run funny and performance could be impacted with an factory ECU but unlikey any damage would result.

The sound get really-really-really old really quick if you're older than 17.

 

Hmmm... I'm almost 21. :P It was just an idea... but would not add if could affect performance in a negative way. It's just that the psssst sounds freakin awesome between shifts! Hahahaha...

 

No way! Nothing beats the sound of Tial wastegates! BOV 's are annoying. Although the super sequential blow off valve by HKS is pretty cool sounding.

Unlike other blow off valves that are push type, the SSQV will not leak under high boost conditions nor under vacuum at idle supposedly.


If you can deal with people saying "Hey, I think there is a turkey stuck in your engine bay" then I guess this is a good BOV for you. The sounds resembles that of a turkey getting hit by your car but its still rather cool. Id suggest getting the lower tone kit to make it not so high pitched sounding. Then it will sound more like a Greddy Type S.

 

^^ no, hehe, some cheap BOVs sound like tortured turkeys...a good 100sometin dollar BOF sounds amazing

Oh, neither BOF nor wastgates affect performance negatively...it just prolongs the turbo's life...DA zit yo!

The turbo is gonna keep blowin as long there's exhast flowin, and as soon as the Throttle body's butterfly opens you got boost. There's 0.000000000001s dalay that the air takes to make pressure again inside the engine but if thats a problem then just suicide. <---not a suggestion

peace to all of those in FL this weekend!!

 

If the BOV ONLY prolongs the turbo's life, then why don't manufacture include it stock? Coz the noise might not be for everyone?

 

I really dont know why manufacturers dont do it, i can tell you that there ARE BOVs that release the pressure much faster with a bigger valve and the sound is so minute that it blends with the engine's noise...these are MUCH more expensive.

Tru the noise isnt for everyone, actualy i bet most people detest the noise, but I REALLY LOVE IT...infact, if i were ricy enough i'd put a horn/speaker that went pssSSST b/w shifts!!

 

Most factory turbo vehicles include a blow off valve stock. There are three general types of valves:

1) Recirculating: The valve vents the air back into the intake. This is quiet and usually isn't audible. (This is what most turbo cars have stock from the factory)
2) External Venting: This is the aftermarket Fast and Furious valve which dumps the externally and usually is engineered to be loud.
3) Hybrid: Recirculates % into the the intake and % externally. This gives you some noise while still keeping the ECU happy by dumping air back into the intake that is expected.

BOVs are usually a total ricer mod.

 

BOV's help with bigger snails.... most stock cars dont need them until they upgrade the turbo....

 

Name a single stock modern turbo car that doesn't have a BOV from the factory. There is so much misinformation on this forum.

 

pimpest noise is a bof with a wastegate so it gets the vrrrrrrrrrom pst pst pst pst flutter

 

The flutter noise is an incorrectly adjusted BOV.

 

Some aftermarket BOV's will cause a fluttering noise with certain ball bearing turbos and are still tuned properly. Ball bearing turbos can take a small amount of compressor surge (or shock) and still be fine, however journal bearing turbos will have their centersections go bad over time with enough compressor shock.

Manufacturers dont call their valves that release built up pressure in the intercooler piping "BOV's", most of the time they are referred to as recirculation valves. If you dont have some kind of recirc of BOV, the turbo will be destroyed after a few hours of driving.

Atmospheric BOV's on MAFS (Mass Air Flow Sensor) controlled vehicles (Nissan's, etc) will tend to be bad for the drivability of the car because the metered air that the ECU thinks it is about to burn will instead be jetted to the atmosphere, thus causing a slight rich condition and stumble during shifting. Furthermore it is more than likely to cause the engine to stall when coming off the gas and going into neutral. Atmospheric BOV's on other applications like MAPS (Mass Absolute Pressure Sensor) controlled vehicles (Honda's, etc) don't cause any real problems since the ECU is getting its input from inside the manifold after the throttle body.

An improperly tuned BOV (one that leaks under full boost, or doesn't release when pressure has been built up) will eventually destroy the turbo quicker and thus can be bad.

This isnt true, every turbocharged vehicle has turbo lag. Just because there is exhaust present doesnt mean it is enough to drive the exhaust turbine. Generally smaller OEM turbocharged vehicles the car will not reach full boost till about 3000 RPM's, and some may never reach full boost in first gear because of the gearing.

 

I was at an auto-x recently where there were tons of STis and Evos and man, those BOVs are annoying. It was driving me crazy. I typically love the sound of cars, but I can't understand how anyone can deal with that. It was nice when the Porsches were running. Wow, what a difference.

 

I've seen and heard fake blow off valves that companies now sell. Pathetic.
But as stated earlier, it's to release pressure. Sounds damn cool too on high-HP cars.