wastegate dumping. . . been there doing that

[Ken Keith]

Sounds like they were talking about a blowoff valve, or a bypass valve vented to
atmosphere.  That affects the air in the intake between the airflow meter and
the throttle body, or more specifically the air in the intake between the turbo
and the throttle body.

The gases from the wastegate that is currently being discussed is after it's
been through the motor, and is "excess" (after the desired boost level is
achieved) so it is let out of the exhaust manifold without going through the hot
side of the turbo and thereby making it spin faster.  Normally it is routed back
into the downpipe, bypassing only the turbo but going back into the rest of the
exhuast system.  This potentially causes turbulence and adds backpressure
in the exhaust.  Other options for dealing with this extra gas from the
wastegate are running a separate pipe all the way to atmosphere (by the
main tailpipe for example) from the wastegate, or letting it out in the engine
compartment (which to me seems nasty and generally not a good idea).

Using a blowoff valve or bypass valve vented to atmosphere in the intake system,
causes an over-rich condition, since the air that is being let out was measured
by the CIS, so it thinks it's going to get into the motor and injects the amount
of fuel that would have been appropriate.  This can mess up the cat, and/or make
cool-looking exhaust flames in certain circumstances I think.

The blowoff or bypass valve only gets actuated upon shifting, when the throttle
almost closes and the pressurized intake air has nowhere to go except back to
the turbo, slowing it down and adding load onto the bearings.  So, using a
bypass or similar device recirculates or vents this pressure so that the turbo
can stay spinning and ready for when the foot presses on the go pedal again.

Even more technically, I believe a true blowoff valve might be a pop-off valve,
or a valve that stays closed except for bad situations where there is too much
boost in the system due to a malfunction, and acts similar to a fuse or circuit
breaker, sparing the next weakest link in the system the damage from
overpressure.  There is some mincing of words somewhere, between blowoff valve,
and BOV, or some other name that I forget.  This is perhaps a third type of
intake pressure valve, and it isn't used for the same purpose.

I hope I got that right.

Ken

Schwnnbkr1 at aol.com wrote:

<<What ever happened to all that about this melting the catalytic converter?
You guys had me convinced this was wrong! Anyway, is this possible on the
type 44s or would there be a problem there (like melting the cat,or fouling
the O2 sensor or likewise)?. That certainly must sound cool though.>>