Newsgroups: rec.autos.tech
Subject: SHELBY PERFORMANCE UPGRADE CHIP -- ILLEGAL?
From: dave.williams@chaos.lrk.ar.us (Dave Williams) 
Date: 25 Sep 92 01:49:00 GMT
Reply-To: dave.williams@chaos.lrk.ar.us (Dave Williams) 
Distribution: world
Organization: The Courts of Chaos * 501-985-0059 * Public Access Usenet


-> uncle had put one of these chips in his Mustang, I think,

 I'd be *very* surprised if a Dodge chip would work in a Ford.


-> 1-Is a chip swap really all that's needed, even for a
-> completely different make of car?

 If you have a car with a computer controlled automatic transmission, a
chip swap *may* help.  For a manual - at least with GM - the chips are
IMHO worthless.  We checked several on a friend's Corvette with zero
difference at the strip.


-> 2-If a chip swap is indeed all that's needed, what's to
-> stop the common yokel from getting hold of a ROM duplicator
-> and doing it himself?  Not that I would ever try such
-> a deed ;-).

 Most of the schemes use an EPROM "carrier" package, with the chip in
that.  You could probably scam some packages from a junkyard.


-> 4-HOW would this be accomplished?  Altering the fuel mixture,
-> or spark plug fire timing, or what?

 Let me explain how a GM Tuned Port system works:

 The injection system normally runs in closed-loop, monitoring air/fuel
mixture via the oxygen sensor.  The computer adjusts the spark advance
according to data maps (cells) stored in the EPROM chip.  It uses
various inputs to determine which cell to use - throttle position, temp,
pressure, etc.  These data cells also control shift points and some
other odds and ends.  A feature of the GM system is that the cells are
self-programming to a degree.  If there isn't a cell which precisely
matches the input requirements, the computer will "learn" fudge factors
to get back on the map.  That's why some cars run like crap if you
disconnect the battery very long - the computer "forgets" the fudge
factors.  At wide open throttle, the computer goes to open loop, sets
the air/fuel mixture to a guesstimated rich position judging from mass
airflow or speed/density (depending on the particular installation)
instead of watching the oxygen sensor.  The sensor is only good over a
limited range; it can't tell how *much* the mixture is rich (maximum
power is slightly rich).  Finally, the computer slams the spark advance
all the way to max, usually 20 degrees, and then lets the knock sensor
keep the thing from detonating itself to death.

 As you can see, the computer basically keeps the engine at a
stochiometric (properly balanced) air/fuel ratio most of the time, and
fiddles with the spark for emissions purposes.  At full throttle, it
goes to rich and maximum advance.  The only thing a chip can do is
diddle with the advance while running at stochiometric - that's what
Hypertech's chips, or at least the ones we played with, do.

 It should now be obvious that no chip is going to do anything to a
Tuned Port, at least as far as maximum power output.  The stock
programming is *already* set for maximum power.  For part throttle, it
will depend pretty much on how sensitive your particular engine is to
spark timing - you might be interested to know GM pushes close to max
advance most of the time, even though you theoretically want a retarded
spark for most emissions purposes.  That's because most gas is so crappy
you hit the detonation limit before you go off the smog curve.

 The TPI is the only system I know very well, but I'd make a wild guess
and say the Dodge and Ford systems probably don't work much different.


[note] Before anyone wonders why I'm talking about speed/density along
       with Tuned Port stuff, the GM manuals we used to research the TPI
       mentioned speed/density as well as mass airflow, though I've
       never seen an example of a speed/density Tuned Port.

=======================================================================
can you help me...help me get out of this place?...slow sedation...
ain't my style, ain't my pace...giving me a number...NINE, SEVEN, EIGHT
(Nazareth)               XJ900 TURBO at 15psi          DoD# 978  KotFAQ
=======================================================================
     
From: dick@hpscit.sc.hp.com (Dick Lucas)
Date: Tue, 29 Sep 1992 16:28:32 GMT
Subject: Re: Oil Pressure Relief Valve ?
Organization: Hewlett-Packard, Santa Clara, CA