[BiturboS4] BOV v. DV

[Ian McCloghrie]

On Jul 19, 2002 Todd Sager wrote:
> ECU from incorrectly adapting the fueling.  With a BOV, the ECU sees air
> being pulled through the MAF, and assumes this air is being used by the
> engine, when in fact it is being vented to atmosphere.  This leads the
> ECU to add fuel unneccessarily, which begins to degrade drivability.

The primary problem with BOVs that vent to atmosphere is that,
generally, they leak.  This means that under partial throttle (without
boost) you will be sucking air IN through the BOV, probably unfiltered,
and bypassing the MAF sensor.

If a vent-to-atmosphere BOV can be designed to seal properly when
closed and only open when there's vacuum in the intake manifold and
boost in the intake tract, it can be used with a MAF car.  Yes, it
will release some of the measured air to the atmosphere, but that only
happens on throttle liftoff.  At that point, the computer has sensed
the closed throttle, and shut off the fuel injectors anyway.

All that being said, there's really no reason to go and replace your
S4's recirculating bypass/diverter valves with vent-to-atmosphere ones
unless you want to make it louder.

--Ian