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In a message dated 96-01-06 17:42:51 EST, you write:
>Someone hac mentioned going to great lengths swapping various parts,
>and such to prevent leaning out.
>Are you sure you ARE leaning out?
Yes, that comment is made with the A/F installed..... Common knowlege is
that given the "stock" perameters of the fuel system with no mods an early
urq tops at about 275-300hp and a 86-89 1/2 5ktq tops at 330-350...... The
biggest prollum is the turbo mods more than engine mods...... My lean spot
is before the car reaches redline, in fact midrange rpm full throttle make a
serious lean condition.....
>On my Xr and others I know we have been using the Air/Fuel indicator from
>A little black box you can wire into the O2 sensor. You can add a heated
>but on an Xr exhaust gas temp is hot enough at idle, 800 degrees for a
>Past 3000rpm on the Xr you switch to open loop and run on the ECU map. An
>may have enough heat already not to need an extra heated sensor. You need
>least 600 degrees to get the O2 sensor to read. That is what all my gauges
>The A/F gauge is dead till my exhaust temp gauge goes to 600+.
all audis since 1986 have used the 3 wire (heated) sensor from the
factory..... given it's location on the urq I'm not sure 600 degrees is a
prollum tho, certainly after the first spool of the turbo...... Bosch
technical bulletins indicate a fully operational temp of 650 degrees F, and a
minimum of that for proper sensing......
>Anyway, I assumed that with a big valve ported head, .500+ lift roller cam,
>flow exhaust, more than stock boost, bigger air vane meter etc that I would
>exceeded the fuel flow.
>Not so. Below 3000rpm the lights indicate the O2 sensor keeping things in
>14.7:1 range. Over 3000rpm and into open loop I run about 12:1. Mash the
>throttle and the mixture richens up to 10.5-11:1 and settles down to 12:1.
>holds up to 7000rpm and 17lbs boost. I know people who run more boost and
>haven't leaned out. And I know some who found out they do.
And I have the prollum between 2k and 3.5k, then a higher A/F of about 16:1
at WOT above 3.5k..... This is common..... I can attest to the fact that
if you run a 5ktq with mods over 17lbs you are going lean with the stock fuel
setup..... However, a couple of things to think about.... If you are
taking the reading off the dash, you don't have accurate read of true boost
pressure...... If you have just computer mods, you may not be getting
17psi, and in fact the WG freq valve (86-89 1/2) will add or delete pressure
to the WG to give you only the boost the ECU will allow, tho with a hold
delay of 3 seconds, you may not get a lower reading.... So you may be
running lean the whole time, but the computer is sensing it only by knock or
heat, and if the ecu does it's job, it will regulate the boost based on those
>I would try one of these meters before going ahead with a bunch of extra
>You may not need it. And too much fuel will hurt power output. I just power
>of the lighter and run one wire from the O2 sensor. I attach the box with
>velcro when I want a reading.
Peak power on a lambda system is .86 lambda or 12.6 to 1 A/F..... Peak fuel
economy is at 1.05 lambda or 15.4 to 1...... That means if you exceed
either you defeat more than you think..... 12.6 to me is the best, but you
have a good chance of washing the Cat with excess fuel when that is run for
any length of time beyond full boost WOT..... A reading of 15.4 or more is
dangerous on the other end of the scale, you get high combustion temps, knock
and maybe a hole in the piston running this for any length of time or for a
moment at full boost/WOT
>You can find ads for the TWM meter in Turbo mag, Europian Car and Grass
>Price w/o a heated sensor was $125? I think. A friend has one in his tool
Cyberdyne makes a 10 LED w/o heated sensor for less than half that.... Both
are references, not the true "actual" measure, but with my lambdaless system
it is accurate enough to set baseline fuel mixture....
The point of the guage is well taken tho.... I'm not sure I would run any
mods without knowing what the result of that mod is...... Esp you guys with
the fuel pump ground WG mods that Charlie has earned the MacGuyver Swiss
Cross for..... An A/F meter to the stock O2 sensor is a great idea, cuz it
will tell you what the car is interpreting as fuel....