valve" or "blow-off
valve" (BOV) and a "compressor bypass valve" (CBV) do
the same thing, which is to release compressed air in
the intake tract when the throttle closes, so as to
prevent high pressure from smacking back into the
compressor wheel of the turbo. If the valve vents the
relief air to atmosphere, it's a blow-off valve or dump
if it sends the air back to the intake, it's a
compressor bypass valve. To explain this more refer to the diagram.
When the turbo is working it is drawing in air through the air intake and blowing air at high
pressure into the engine (follow the red line). If you ease off the
accelerator then you are closing the duct (throttle body) through which
this air enters the engine. This causes this high
pressure to bounce back along the route it came from (follow the green line) and
smacks into the turbo thus stopping the compressor wheel
from turning. This is turbo stall. When you
accelerate again the turbo has to get back up to speed
again (spool up). A blow off valve will allow this
excess pressure to be vented to the engine compartment (thick orange line)
thus reducing turbo stall and helping with spool up.
A bypass valve vents this excess pressure into the air
intake on the other side of the turbo (thin orange line) and this not only
relieves the pressure on the compressed side of the
turbo but the increase in pressure on the air intake
side helps to keep the turbo turning.
Go To Blow Off Valve Shop
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