Turbo Question
 

Hello! I have a nooby question about the bov noise on turbo'd cars. I dont have a turbo'd car so I am not sure if this is true or not, but in the videos I see online, why is the bov noise more audible at times then others? Is it the more throttle you give the louder it is, or if you give it to much throttle can you even hear it? I am planning on going FI soon, and was debating on turbo or SC. If the BOV is audible I would go Turbo, but most of the videos I see of TT g's I cant hear the bov noise. The only G that I can actually hear it good is this ST one: (you can hear it at 30 seconds in the vid..and sorry for whoever's vid this is). Does your Turbo'd G sound like his? THanks!:icon17: :icon17:

The BOV is a "blow off valve". It only gets used when you take your foot off the gas. When you jump on the pedal the boost spools up and stays there until you release. Then, all that pressure has to go somewhere because you don't need the boost any more. The BOV vents that pressure to the atmosphere while making the sound of air escaping. If you don't build up a lot of boost (because you don't put your foot down as hard) the sound of the BOV won't be as loud.

Thanks, that clears alot up. But if the BOV only gets used when you take your foot off the gas, how does it get used in automatics?

Doesn't matter. Auto or MT. It's more RPM related. At high RPM the Turbo is "spooling" fast and making pressure. The throttle is open wide and you are feeding that pressure to the motor. When you back off the throttle, you close the "butterfly" valve on the throttle body and all that pressure backs up behind it. Well it's a good idea to vent that pressure some where so you don't blow off hoses and clamps and such. So you set the BOV for, say, 9 psig and and it vents anything above that to atmosphere. Some vent it back to the intake side so you don't hear it as much and some "blow it off" under the hood and that is what you hear.

It differs in automatics because of how the car reacts during shifts. You may not here a BOV on an auto as well as a manual, because us automatics never have to take our foot off the gas to shift, unlike manuals. Depending on quick the driver is at shifting you may hear the BOV more or less due to the time their foot is off the accelerator and thus, the throttle body is closed and air is being vented. If they shift very fast the time the air has to escape through the BOV is very little because as soon as they are back on the gas the boosted air is going into the engine.

Quieter BOVs is also due to (besides their design) the amount of boost being run. Most of the guys in G/Z's only push around 7 or 8psi so of course the same BOV on that setup would be a lot quieter than the same BOV on a Supra pushing 30psi.

As for the SC/Turbo decision, you can have a BOV on a centrifical supercharger and it will also vent to atmosphere like any other turbo car with a BOV, they work just alittle different and that has been covered on here before. While the BOV sound is sweet, don't let it persuade you into choosing an FI system for you. Get what's right for you and what suits your needs!