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At times i do extended idling and was wondering if the turbo is active? Without having much turbo lag I was thinking it might be spinning even at idle....
 

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Always spinning, yes. But then there's the wastegate, which eliminates boost/higher fuel consumption, no? I'm still learning about turbos...
The wastegate opens when the boost surpasses its setting. It's a valve an spring holding closed a bypass to the exhaust. So if you over-boost, the WG opens. There is a WG duty cycle you can view (well I can in RomRaider) it shows what % is necessary to keep it close.
 

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The wastegate opens when the boost surpasses its setting. It's a valve an spring holding closed a bypass to the exhaust. So if you over-boost, the WG opens. There is a WG duty cycle you can view (well I can in RomRaider) it shows what % is necessary to keep it close.
Thanks! If I had just thought that through a little more... Duh.

So, when is there 0 boost at all, if ever?
 

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I can tell you that Boost/vaccum at idle is around -10 according to torque app and doesnt show positive boost until about 10-12% throttle while driving.
 

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So, when is there 0 boost at all, if ever?
At low RPMs, the turbo acts as an extra load on the engine as the exhaust gasses keep it spinning without producing extra pressure or power. As the RPMs climb, the vacuum reduces and then goes into boost where the increased pressure and power produces a net positive amount of power. Somewhere early in that rapid transition is a brief moment of “zero boost” where the turbo neither robs power away, nor does it produce extra power if compared to a naturally aspirated version of the identical engine. That point is roughly where the driver feels the turbo lag end and the rush of the turbo boost.
 

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Someone please correct me if I’m wrong. I am by no means an engineer or expert.

How I understand it is the intake side of the turbo is always spinning when the engine is running and producing some positive pressure to the intake. However at low revs, this positive pressure is negligible in the presence of the vacuum the pistons produce. As the turbo spools up, the pressure increases (boost) to produce a net increase in power. Therefore the only time the turbo is at complete zero boost is when it is not spinning, or engine off.
 

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Someone please correct me if I’m wrong. I am by no means an engineer or expert.

How I understand it is the intake side of the turbo is always spinning when the engine is running and producing some positive pressure to the intake. However at low revs, this positive pressure is negligible in the presence of the vacuum the pistons produce. As the turbo spools up, the pressure increases (boost) to produce a net increase in power. Therefore the only time the turbo is at complete zero boost is when it is not spinning, or engine off.
No.

You got close with your mention of vacuum from the pistons. If the pistons see a vacuum then you would see a vacuum at the boost gauge right at the exit of the turbo (compressor side).

So the turbo is basically a rod on a bearing with a fan on each side. If the engine is running that rod is spinning from the exhaust gasses. But you have to spin it fast enough to make boost. Think of a fan on a windy day, you may have to turn it to high before it actually moves air faster than the wind. So in this car you don't feel it as much but if you get into an older WRX you can just barely get started in 1st gear then floor it and you will feel the motor start to work but you're not accelerating very hard yet, then you may start to hear the turbo get to work (spooling) and right after that you will feel the massive change in acceleration as the pressure slings from vacuum to full boost pretty quickly.

So to your 0psi point you will pretty easily get to 0psi if you are at cruising speed and then slightly give it throttle. If you are accelerating hard then you will pass 0psi quickly on your way to 14.4psi (I think that's what it's set at). Once you are at 14.4psi your turbo could produce more boost but your ecu is not designed for more air. This is where the wastegate kicks in. It will actually open a valve (rapidly as needed) to bleed air back into the intake, behind the mass airflow sensor (MAF) but before the intake of the turbo. This is because that air has already been accounted for they just recirculate it till it is not needed. This is why a blow off valve (BOV) on a stock wrx/sti is a bad idea, you'll run rich because you are dumping that air. How bad is it? Debatable, but it's also an annoying sound imo.
 
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