Blow-off Valves

[Joseph Pizzimenti]

Brandy,
A BOV will vent that pressurized air into the
atmosphere.
A DV or BPV will vent that pressurized air into that
airbox, where it will be metered by the MAF.

If BOV is hooked up, you may run rich on throttle
lift, but with DV/BPV, you should be fine.

Joe

PS -
BOV = Blow off Valve
DV = Diverter Valve
BPV = Bypass Valve
MAF = Mass Air Flow
Joe = Crazy Audiot
--- Brady Moffatt <bradym at sympatico.ca> wrote:
> Hi Steve/All,
>
> I'm starting to learn about all this turbo stuff...
>
> From what I understand, the BOV releases pressure in
> the intake between the
> turbo and the throttle plate when the throttle is
> abruptly closed and the
> pressurized air has nowhere to go. The air "bounces"
> off the closed throttle
> and goes back to the turbo, slowing it
> significantly, and accelerating wear
> on the turbo. With a BOV, the air escapes through
> it, and does not slow the
> turbo as much.
>
> But, BOV or no BOV, the bulk of the air isn't
> getting past the closed
> throttle. So I don't see how the mixture would be
> affected by the BOV.
>
> Am I missing something?
>
> Cheers,
> Brady Moffatt
> Montreal, Quebec, Canada
> 83 UrQuattro with 50,000 miles
> 86 4ksq with 308,000km
> 86 4ksq parts car
> 72 Datsun 240Z with 180,000 miles
> 92 VW Golf with 200,000km FOR SALE
> in middle stages of quattrosis accumulatus
>
> ----- Original Message -----
> From: "Steve Sears" <steve.sears at soil-mat.on.ca>
>
>
>
> > Taka,
> > A BOV will not cause CIS to stall, since the
> opening of the valve will
> vent
> > some pressurized air ("metered air") instead of
> taking air in ("unmetered
> > air" - aka - vacuum leak).  The result will be
> that the mixture will go
> way
> > rich while the valve is open.  I seem to recall
> someone posting about the
> > use of BOV's and CIS - mentioning that if you see
> a VW making the
> > characteristic "ksssshhh" noise, you'll see a
> blast of black smoke from
> the
> > tailpipe when they get back on the gas.  The
> result is a waste of fuel,
> and
> > the premature death of the catalytic
> convertor/oxygen sensor.  But if one
> > subscribes to the "sound and fury" club, and
> doesn't have/need a cat/oxs,
> > then go for it.  Added tip - putting a K&N on will
> also increase
> audibility
> > of the turbo (if somebody wants one, I'll sell the
> one on my garage
> shelf -
> > it's doing a great job of keeping the dust off the
> wood).
> > Now EFI......now that's getting away from the
> .001% hp gains of adding a
> > lighted exhaust tip and into some serious
> stump-pulling.....I suggest
> adding
> > an airhorn to the BOV to announce the presence of
> your "sleeper" :-D
> > Steve Sears
> > 1987 5kTQ - "I wish I had EFI"
> > 1980 5k - "I wish I had a turbo"
> > 1962 and '64 Auto Union DKW Junior deLuxes - "I
> wish I had a four-stroke
> > engine"
>
>
> ---
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