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Re: BOSCH blow off valve

Avi wrote:

> Glen,
> This afternoon I tested the Bosch valve with a calibrated gauge (attached
> to a regulator), results are:
> 1.valve is totally closed up to 5-6 PSI
> 2.valve start to open at 5-6 PSI
> 3.valve stays partially open till 20PSI (did not test it any higher)
> 4.valve opens with vacuum (max opening)
> checked two (2) valves side by side, both react the same
> Conclusions:
> 1.valve is not a positive shut off, keeps bleeding after 5-6 PSI
> 2.since valve is not a positive shut off, it should last a long time....
> (my experience says otherwise?..)
> That is the latest for now, more (maybe), to follow
> Avi

Avi,Excellent post!  I am still trying to sort out the conflicting veiws on the
blow off valves.  If you could indulge me for a couple of questions I would
appreciate it.

1.  Does your data mean that two Bosch valve will start to bleed off pressure at
the additive of the two (10-12psi) or that they will bleed off pressure twice as
fast at 5-6 psi?  My assumption of you analysis is that there would be twice as
much bleed at 5-6psi making it more difficult/slower to build boost on the

2.  Have you tested any units, such as the much talked about HKS unit to see if
there is a positive shut off and not the bleed you encountered at 5-6psi?

>From your data, which I would consider a pilot study of this devise, it would
seem that the Bosch unit is designed for low boost applications, not the higher
boost levels that many on the list are using.  Too bad you do not have access to
a large enough sample 8-10 units to make a more definitive claim on the function
of these units and put the blow off valve controversy to rest.

Great work! Thanks,


Randall C. Markarian

1990 V8 Quattro
1996 Merc E320

Saint Louis, Missouri