blowoff valve questions

[Jukka Majanen]

Hi

Chris wrote:
> Has anyone here ever run a blow-off valve instead of replacing their BPV
> when it blows?  I see that many manufacturers use those from the factory
> (Mitsubishi, Nissan, Mazda) and this could help eliminate our blown
> hoses, etc. issues with chipped cars and/or upgraded turbos, since the
> pressure is relieved instead of being re-routed. 

Recirculating, or blowing out, it has nothing to do with blown
hoses etc. When the throtte gets closed, load also decreases
and it is small amount of air to be led out/recirc, just to avoid
surge and/or pressure shock.

> As an aside - those other manufacturers, Mitsu, Mazda, Subaru, etc. have
> blow-off valves AND MAFs.  How is this possible for them but not for our
> cars?

If the airflow/mass is measured after the turbo, at the throttle,
there is no problem because it doesn´t count the air that is
blowed off. I don´t know about those rice cars, but there has
really been some metering in pressure side, not common.
All Audis 5-cyl turboengines 10/20v MC/KG/2and2B/3B/ABY
and what else, have metering before the turbo, when stock.

Achint wrote:
> If the Bypass is replaced with a Blow off valve, metered air will
> get lost and the ECU will assume that there is a leak somewhere 
> in the system.

I don´t think it knows anything about the leaks, it thinks all
is in the engine and will lead to very rich mixture, as seen
in rally cars.

With nice sound Blow Off will: 
reduce lag, but toast cat... hmm -poetry :)

regards
j-pm
MC with +1.1 Bar charge and Bosch -200 mBar By Pass