what is a shrapnel knob?

[Robert Myers]

The shrapnel knob is a small gas pressure regulator used to provide 
(boosted) manifold pressure back to the wastegate cap above the WG 
diaphragm.  This adds air pressure to the top of the WG diaphragm and acts 
as if a stiffer spring had been inserted in place of the stock spring.  In 
order for this simple mod to have the presumed desired effect of increasing 
the maximum boost available for the engine it is also necessary to use some 
means of modifying or eliminating the OEM overboost protection.  This can 
be accomplished in several ways.  One very simple, if perhaps risky, way is 
to do the infamous resistor/zener mod which prevents the ECU from knowing 
what the actual boost level is by electronically clamping the output from 
the pressure transducer to an arbitrary (zener dependent) level below the 
cut-off level.

The shrapnel knob is convenient because it allows easy adjustment of the 
maximum boost level by simply turning the knob of the pressure 
regulator.  This pressure regulator can even be installed inside the 
cockpit where it can be adjusted on the fly if so desired.


At 07:54 AM 12/6/2003 -0800, CL Wong wrote:

>Yes, I've checked the archives.  Lots of folks have
>them but haven't found any references on how to build
>one and what it does.
>
>I came across this article at autospeed and the phrase
>'shrapnel knob' came to mind.  Is this the same thing?
>
>http://www.autospeed.com/cms/A_0670/article.html?popularArticle
>
>Looks interesting and I'd like to try building one for
>my 20020v for kicks.
>
>
>thanks
>
>Chi
>
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Bob
*****
  Robert L. Myers 304-574-2372
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