what is a shrapnel knob?

[Eric]

Brett Dikeman wrote:

> At 7:54 AM -0800 12/6/03, 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.
>
>
> It just progressively restricts how much the wastegate can close.
>
> It's also incredibly stupid, considering that you can neither hear 
> pinging until it gets engine-damaging bad, nor react fast enough once 
> you do.
>
>> Looks interesting and I'd like to try building one for
>> my 20020v for kicks.
>
>
> Extremely stupid idea.  If you don't blow the engine, you'll overspin 
> the turbo- get a chip instead.
>
> Brett

Rather harsh don't you think? 

Chi the shrapnel knob is as Robert Myers replied.  I don't know where 
the name comes from, but I could guess.  As you likely read in the link 
you referenced that modifciation is different.  It has two features.  
One is a regulator to control the overall boost and serves a similar 
function to the s. knob, but it regulates the actual air pressure from 
the manifold on the lower side of the waste gate.  The second feature I 
think is quite clever.  The adjustable blow off valve eliminates the 
tendancy for the WG to open partially at partial boost.  As the author 
describes he saw dramatic improvements in performance without any 
additional boost just because the turbo spooled so much faster.

As long as you are reasonable in the boost levels you run and use good 
gas you will have no problems with pinging.  Overspeeding the turbo 
happens when you in simple terms ask too much boost of it.  I can't 
speak as to how your 20v will behave with additional boost, but I 
believe it will start to cut fuel if you ask for too much boost.  I 
don't want to guess on that.  I would think the ECU would cut fuel 
before you could overspeed the turbo.  Anyone who knows more about the 
20v ECU would better answer this.

I plan to do the same thing to my car as described in that article once 
I get my new engine fully broken in.  As long as I keep the old CIS I 
don't plan to push too much boost.  I am going to wait for EFI for that.

Good luck


-- 
Eric Sanborn
'85 4ktq

http://www.sofadog.net/4ktq/