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Garrett Turbo Tech 103
Surge is most commonly experienced when one of two situations exist. The first and most damaging is surge under load. It can be an indication that your compressor is too large. Surge is also commonly experienced when the throttle is quickly closed after boosting. This occurs because mass flow is drastically reduced as the throttle is closed, but the turbo is still spinning and generating boost. This immediately drives the operating point to the far left of the compressor map, right into surge.

Surge will decay once the turbo speed finally slows enough to reduce the boost and move the operating point back into the stable region. This situation is commonly addressed by using a Blow-Off Valves (BOV) or bypass valve. A BOV functions to vent intake pressure to atmosphere so that the mass flow ramps down smoothly, keeping the compressor out of surge. In the case of a recirculating bypass valve, the airflow is recirculated back to the compressor inlet.
PTB problem is "surge under load." not good.
 

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duster360 said:
Garrett Turbo Tech 103
Surge is most commonly experienced when one of two situations exist. The first and most damaging is surge under load. It can be an indication that your compressor is too large. Surge is also commonly experienced when the throttle is quickly closed after boosting. This occurs because mass flow is drastically reduced as the throttle is closed, but the turbo is still spinning and generating boost. This immediately drives the operating point to the far left of the compressor map, right into surge.

Surge will decay once the turbo speed finally slows enough to reduce the boost and move the operating point back into the stable region. This situation is commonly addressed by using a Blow-Off Valves (BOV) or bypass valve. A BOV functions to vent intake pressure to atmosphere so that the mass flow ramps down smoothly, keeping the compressor out of surge. In the case of a recirculating bypass valve, the airflow is recirculated back to the compressor inlet.
PTB problem is just like the surge described above but at half throttle.


Or another way to put it, is because the wastegate stays closed, and the boost builds too fast (faster than it is being released from the compressor housing) and the air actually starts being released back through the turbo in the wrong direction.

Edit: Took this out of a book I have,

"Surge is the situation when the compressor "spits out" more air than the engine can swallow, which causes a backup of air at the intake and it actually creates reverse-flowing pressure waves that can be very damaging to the turbo. You want to avoid surge at all costs."
 

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or a flutter type sound that you can hear very well when you have an intake. there is a guy near where i live and he swears its his BOV and he loves the noise it makes. im just sitting back waiting for it to take a dump so i can say "told you so you sorry basterd"

but its like they said above , too much air going in so it wants to come back up the way it came. kinda like drinking too much!!
 

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The bad surge happens under WOT or when you have too much PTB. The stock surge valve and an intake will make this sound but that is ok. Its also known as a horse laugh. My HKS SSQ does the same makes the same sound when it releases light loads of boost.
 

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:rofl: :rofl: :rofl: that's the best analogy i've heard yet haha


blackhawk said:
or a flutter type sound that you can hear very well when you have an intake. there is a guy near where i live and he swears its his BOV and he loves the noise it makes. im just sitting back waiting for it to take a dump so i can say "told you so you sorry basterd"

but its like they said above , too much air going in so it wants to come back up the way it came. kinda like drinking too much!!
 
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