Re: cheap power

[QSHIPQ@aol.com]

In a message dated 97-05-12 15:07:18 EDT, you write:

<< If air density affects the flap/chamber fuel/air curves then, as Phil
 Payne suggests, then wouldn't less dense air cause a rich condition?
 
 What I'm really getting at is would us high altitude Quarrto owners (ie
 Denver) benefit from a "ram" air effect into the air box by compensating
 for the less dense air at this altitude?
  >>
No, because most CIS systems have altitude compensation in them, 2 ways in
fact.  1) a lot of the audi cars have altitude compensation in the control
pressure regulator.  Specifically, there is a port for Po (atmospheric
pressure) that increases control pressure as you gain altitude (leaning the
mixture, since more air is required as you increase altitude, more
specifically, less fuel is required as altitude increases).  Most Lambda cars
really don't need them though (and the main reason the port isn't always
found on the later cars).  The lambda circuit measures the amount of "excess
air" in the exhaust, and adjusts the O2 frequency valve to either increase
fuel or decrease fuel to the injectors.  The less air at altitude is
compensated by less fuel.

So, as you increase altitude, the amount of oxygen decreases (rich), so the
O2 freq valve returns less fuel to the tank, reducing the fuel going to the
injectors.  As you decrease altitude, the amount of oxygen in the exhaust
increases, and the O2 freq valve returns more fuel to the tank, increasing
the fuel to the injectors.  Mass Air EFI systems operate the same way,
sensing O2 in the exhaust as altitude increases and reducing fuel injector
"open" time until 1.00 lambda is reached.  

Turbo cars just compress more air into the cylinders, so they are "altitude
compensating" or Absolute pressure engines.  That is to say, as altitude
increases, so does the amount of boost required by the turbo to get the same
amount of air into the cylinders as at sea level.  Hence why turbo cars are
less affected by altitude than N/A cars.  (more on this is in archives - very
nerdy).

So to "ram" air, tho sounds good, really doesn't have any accuracy to it in a
CIS car.  The ram effect varies by speed, so your air supply at Po or Px
(insert speed here), is not a constant, and your lambda circuit will go nuts,
as will the control pressure compensation.  Best to leave it alone, any gains
you think you have really are just changing Px+/- (speed variable) in an
equation that by design is SUPPOSED to be Po only (and a constant). I bet I
could put a finger on the bottom of the flap and get a better A/F ratio than
a "ram air" design.

I'm waiting for Probst to whack me on the head.  Get the book folks, it's a
lot simpler.  The myths and legends and homebrews of CIS/EFI can all be
elightened from this reference material.   A lot of information, and a great
source to learn about FI, CIS and/or EFI.  Tweeking FI takes a lot of
research, and they aren't easy answers.  The losses in hometweeks outweigh
most of the "simple" gains.  

HTH

Scott