Recirculating BOV

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squiggy

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Toyota MR2 Spyder
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A question for all of you turbo knowledgeable people:

Any benefits by using a recirculating BOV versus vent-to-atmosphere BOV? Is setup/installation/tuning more difficult?
 
I haven't a clue.........
That being said, I'm guessing temperature would be warm recycling, and cool going with ambient air......... Soooo....... ???????
 
V-T-A for that "turbo" sound. I mean, that's the real reason to get it isn't it? hhahah. I really don't know. I bet Vit would be best to ask.

Also, you need to install a nitrous purge valve.

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The thought behind using recirculation is that diverting the pressurized air back to the turbo will improve it's response when getting back onto the throttle after a shift.

Compared to a VTA setup, it's more complicated only because you have to:

1) Have a BOV/BPV that has a fitting for a recirculation line.
2) Run said line between the BOV/BPV and the turbo inlet.

As always, if you are switching from one setup to the other, you will need to go back and get your tuner to account for the change. If you look at other platforms (Subarus and Mazdaspeeds are notable examples), you'll notice people who switch out their stock BPV for a VTA BOV without getting their tune looked at getting a lot of grief. This is because there is almost always a "rich condition" that happens when you let off for the shift due to the ECU being confused by the change.

Also because, like I mentioned in the beginning, it hinders performance and therefore, it's considered a "ricey" thing to do.

As always though, it's your car, so do whatcha gotta do.
 
Monk said:
I haven't a clue.........
That being said, I'm guessing temperature would be warm recycling, and cool going with ambient air......... Soooo....... ???????
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It would be going through the intercooler though.
 
squiggy said:
What exactly hinders performance?
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I think it's the fact that the turbo can use the extra air in a recirculating setup for a little more power whereas in a vent setup, it's wasted potential.
 
Its because the extra air thats recirculating is pressurized so that the next time the throttle body is opened its forced into the combustion chamber. Kind of like the scavenging effect from a properly sized exhaust. And the air is cool because its air that has already been through the intercooler. They sit just before the throttle body and they're purpose is to relieve the pressure thats built up when the throttle body is shut while the turbo is still spooled up. Without either that air pushes back through the turbo and can stop its spinning and even cause it to reverse which builds up heat and is super hard on the bearings.

The only reason to go with a blow off valve (non recirculating) vs a bypass valve (recirculating) is if your pushing enpugh boost to cause this turbo flutter even when the bypass valve opens.

That's about as much as I know. I would think to run a bypass valve you would have to have some sort of chamber to bypass through, which any aftermarket intake wouldn't have, but this is just speculation.
 
Bulkybear said:
Its because the extra air thats recirculating is pressurized so that the next time the throttle body is opened its forced into the combustion chamber. Kind of like the scavenging effect from a properly sized exhaust. And the air is cool because its air that has already been through the intercooler. They sit just before the throttle body and they're purpose is to relieve the pressure thats built up when the throttle body is shut while the turbo is still spooled up. Without either that air pushes back through the turbo and can stop its spinning and even cause it to reverse which builds up heat and is super hard on the bearings.

The only reason to go with a blow off valve (non recirculating) vs a bypass valve (recirculating) is if your pushing enpugh boost to cause this turbo flutter even when the bypass valve opens.

That's about as much as I know. I would think to run a bypass valve you would have to have some sort of chamber to bypass through, which any aftermarket intake wouldn't have, but this is just speculation.
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So, from what you and BWill are saying, recirculating would be the better choice. If recirculating is the better choice, I wonder why PRL only offers a VTA BOV in their dropdowns?
 
Usually its because of boost levels and aftermarket intake designs not allowing for recirculating valves. Blowoff valves don't inherently lose anything. Just think of bypass valves as having a gain of throttle response over baseline.
 
So, if I understand correctly, there would need to be a port in the intake piping for it to work correctly.
 
PRL and other companies do not offer it mostly due to it adding cost to the kit for what probably is not a big performance difference for most people.

Plus people often think that you won't get any sound with a recirculation setup (You will, as it's venting into the inlet which is obviously open at the filter) and a lot of people want everyone to hear they have a VTA setup.

Also, you do not need an expansion chamber. The air will just go into the turbo (which is obviously still doing it's thing during the shift or after you've let off throttle).
 
BWill9886 said:
The air will just go into the turbo (which is obviously still doing it's thing during the shift or after you've let off throttle).
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Isn't this what a bypass and blow off valve is for? To prevent this. Turbo flutter can damage the turbo pretty easily.
 
My bad. I think my confusion is I thought the bypass valves vented into the pipe that sits between the intercooler and throttle body. You're saying they vent into the air inlet? Are there different kinds of recirculation?
 
Bulkybear said:
Isn't this what a bypass and blow off valve is for? To prevent this. Turbo flutter can damage the turbo pretty easily.
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You are correct, but misunderstanding what part of the system causes "turbo flutter" (what is actually happening is called cavitation). This happens when the air is not released from the charge piping via a BOV/BPV and heads back into the compressor housing. That obviously is not good.

However, we are talking about air in the inlet to the turbo (pre-pressurized) and not the charge piping carrying the pressurized air. Therefore, no such action can occur.

Now, people have raised points regarding the effects over time of this pressurized air hitting the face of the compressor wheel as a potential issue. Though considering this setup is run on basically every OEM turbo application, I think it's safe to say that's not something most of us need to worry about.

Bulkybear said:
My bad. I think my confusion is I thought the bypass valves vented into the pipe that sits between the intercooler and throttle body. You're saying they vent into the air inlet? Are there different kinds of recirculation?
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You got it! That is the only recirculation method.
 
Got it. Since this occurs when the throttle body is shut im assuming this can act like a mini anti lag and helps to keep the turbo spinning when the throttle is snapped shut, like when shifting. Other than that i really can't see a benefit over a vta bov other than less noise.
 
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