Re: more boost

[Robert Houk - SMCC Bos Desktop Hardware <rdh@UrQ.East.Sun.COM>]

   >Here I have to disagree. The Zener has essentially clamped the pressure
   ...
   >WRONG !!!  you loose ALL BOOST PROTECTION !!!!!

   Wow, you guys love to pick a fight!!!! So all those experts who know better
   than me lets see the correct way to do it posted on the list.

   For all the others, remember that the boost sensor will only measure 15 PSI.
   If you remove the boost limit, you will remove the overboost protection. The
   dynamic impedance of a zener diode (hands up everyone who understands that)
   will allow the voltage to rise to 4.5v, just below the cutoff and thats as
   close as you can get without problems and without a lot of electronic
   engineering.

   I don't care what else you do, if you raise the boost cut level, you are in
   danger of losing the overboost protection, because the actual limit is so
   close to the limitations of the pressure sensor (4.65v boost limit, 5.0v
   sensor limit), so go ahead and remove the limit and the overboost
   protection. At least you know its gone and can make allowances for it.

If you claim that all the safety systems remain intact, then you should
qualify that by "all" you do not mean what most English-speaking people
mean, but rather you mean "most".

   Finally I would prefer to have no protection against a diaphragm split( the
   way you guys go on, one would think the roads are littered with dead Audis
   with split diaphragms) than risk detonation by advancing the ignition timing
   under boost. If you are going to put a divider in there and then remap it,
   why the hell don't you just change the software to move the boost limit up?

Because software alone is *NOT* enough. As configured, the boost sensor
pegs out at about 1.1Bar (about 16PSI) boost. That's "5.0" volts, or 
unsigned 0xFF in the 8-bit scale the ECU uses. The sensor however con-
tinues to measure fairly linearly well past 16PSI, but at a voltage that
has exceeded the ECU's A/D reference voltage, so it can't measure it.
Since it can't measure it, the ECU cannot adjust timing for boost levels
past (effectively) 1.0 Bar of boost (nor can it detect overboost condi-
tions past 1.0Bar of boost). However, by scaling the manifold pressure
transducer output voltage you can extend the ECU's "range" into the
low 20PSI's (which is farther than I am going to run *MY* engine), which
easily allows those of us who have some idea what we are doing to run
(say) 18PSI boost, with a 20-22PSI overboost cutoff, with proper ignition
timing across the entire engine operating range (for example, allowing
full advance at a mere 12PSI, while retarding the timing further as the
manifold pressure continues to rise).

   I love experts

I am speaking specifically about the UrQ's MAC-02 ECU, the only one I
have studied, and from what you post above, I am willing to bet I (and
by extension the "network" of those of us who have spent considerable
time and effort in understanding the whole system) know a hell of a lot
more about it than you do.

					-RDH