Blow off valve

[einarp]

>From what I read, the blowoff valve is there primarily to
relieve the compressor impeller from the shockwaves it generates
when it does not "move air" because the throttle is suddenly shut.
It "stalls out" as you would say if it was an airplane wing.
In other words it will give the turbo a longer life.
My source in fact showed a curve where the turbo speed decreased
_faster_ with a blowoff valve (on a Porsche). Probably because it
pumps more efficiently when not stalled, and the backpressure is
still there.

Blowoff to atmosphere is better than recirculation because the
heat rise is lower. But a problem if there is an airflow sensor
before it.

If the blowoff valve were controlled by the engine management unit,
the blowoff valve could be opened _fully_ when going off throttle.
(The EFI unit already have the data to detect this condition.)
Then the turbo should have less resistance and keep the speeed.
Right or wrong?


--
einarp at ade.no  ( Maserati Biturbo Spyder )