manual boost controllers, and ECU functions

[Ken Keith]

I've been doing some research on manual boost controllers.  Wow, 
there's alot you can do with them.  I now know a little bit about 
wastegate creep, and cracking pressure and such.

It seems on some cars, an ur-S4 in particular, some pneumatic 
valves can be added that will cause the wastegate to be held 
closed until the desired boost level is achieved, rather than have it 
start to open earlier, before target boost.  And you can also 
regulate the pressure the wastegate sees, so you can manually 
control max boost.

This seems desirable.  Are there any reasons why this is bad?  I 
saw some references to a momentary 1 or 2 psi boost spike when 
the wastegate opens, or when something happens.  Is that a 
problem?

I was wondering what it is that the ECU on, for example, and MC-1 
motor really does.  I think it basically controls timing, by retarding 
it if it detects knock, and also controls the frequency valve (?, or 
something) to keep the mixture as close to stoich as possible.

But since the fuel injection is mechanical, the ECU only has to 
deal with the fine tuning, and the bulk of the fuel metering is done 
as a function of the airflow plate.

I guess my question is, what does a chip do besides raising the 
overboost fuel cutoff?  I know there are supposed to be some mods 
to some "tables", but what tables are these?  These are fuel 
tables, ignition maps, or what?  Does the ignition get adjusted 
when it's not knocking, perhaps relative to boost?

Check out this webpage:

http://www.autospeed.com/C_articles/A_0685/P_1/article.html

To see the other pages to the article without being a member, edit 
the location to read (for page two, for example):

http://www.autospeed.com/C_articles/A_0685/P_2/article.html

Another question, would an SJM chip affect how quickly target 
boost is reached?  I mean, does it hold the wategate completely 
closed until the target boost is achieved, and only then begin to let 
it open to keep the turbo from overspinning?

If not, it seems like this boost controller setup would be beneficial, 
even for chipped cars.

Thanks,

Ken