Re: Bypass valves and turbos

[QSHIPQ@aol.com]

In a message dated 9/19/99 11:56:55 AM Central Daylight Time, OorQue@aol.com 
writes:
> Although this is a from a Dodge turbo site, it has some interesting info 
>  about these valves in general as well as about why the Bosch valves tend 
to 
>  fail quickly and for other reasons, aren't necessarily the best choice.  
>  Also, don't forget that on turbo Audis, the bypass valve should NOT dump 
to 
>  the atmosphere since the air has already been metered... 
>  
>  Check it out: http://minimopar.simplenet.com/perf/bov.html

An interesting site indeed Jeff.  A couple of issues to consider.  I put a 
post up quite a while ago on the Bosch bypass valves.  My recollection is 
that the spring on the stock audi bypass valve cracks at 6 psi, however let's 
do the math based on 9psi and the double ck valve loop found on the above 
site.

Hoppen stage III 26psi maximum boost altitude corrected.

26/2 = 13 (assuming half the boost goes to the valve, the other half thru the 
1 way ck valve on boost)

13psi + 9psi (baseline spring pressure in terms of boost) = 22psi

Conclusion:  Valve will leak above 22 psi

Let's try a 2.5bar mod

22.5/2 = 11.25
11.25 + 9psi = 20.25

Conclusion:  Valve will leak above 20.25 psi

Let's try a 2.0 bar (14.7psi)  mod (10vt stage II)

14.7/2 = 7.35
7.35+9psi = 16.35

Conclusion:  Valve will stay closed during all operating boost.  Good mod

Let's try a stock 20vt 2.1bar (overboost to 16.17psi) stock computer

16.17/2 = 8.065
8.065 + 9psi = 17.065

Conclusion:  Really close, but sure looks to work.

SUMMARY:  This mod should work on the stock 20vt car, and should work on the 
10v stage II cars (though I've seen some stage II's run in excess of 16psi, 
so that would be a conditional "should work")

NOTE:   If the stock valve indeed opens at 6 psi, this ck valve mod will not 
work on any of the above.

HTH

Scott Justusson
QSHIPQ@aol.com