EGOR Sneek Peek

[Garfield Willis]

On Tue, 16 May 2000 23:46:11 +0200, "Axel Rietschin"
<Axel_Rietschin at compuserve.com> wrote:

>Euh... just curious: are you really checking the gases _after_ the catalytic
>converter?

Uh, yup, we REALLY are!, but I'm glad you asked about that, since I find
I have to remind/revisit that issue every so often for those who missed
the last time this was discussed. Here's a quote from a previous post:

>On Sun, 9 Jan 2000 15:16:52 +0100, "Anders Grop" <anders.grop at telia.com>
>asked:

>>... is this perhaps why mwignitions has put the sensor in the end of exhaust pipe?
>
>Nah, I don't think so; the reason for the use of probes is ease of use,
>primarily. You rely on the cat in the system being ineffective at the
>WOT op points you're measuring your open-loop fueling at (say during an
>extended hill-climb), and so other than lowered ex gas temps, the mix
>you see at the tailpipe is the aggregate uncatalyzed mix out the exhaust
>ports. No additional bungs to add to the header pipe(s), basically. But
>it's only usable during engine ops that leave the cat essentially outta
>the picture.
>...
>BTW, the probe pipe also needs to have enough "aft end" past the sensor
>for another reason, too. You don't want fresh air reverting and mixing
>with the sample you're reading, which is why the aft end of the probe
>needs to be at least around 8-12". The probes I've seen used by two
>diff. vendors really look to be cutting theirs a tad short on the aft
>end, but you could certainly play with the length to see just exactly
>how short you can get away with. Once the readings don't change much
>with further lengthening of the extension, you're there; but better to
>err on the side of plenty long, methinks. Of course, the pickup/entrance
>end of the probe needs to be shoved up in far enough that no reversion
>happens between the actual tailpipe and it, but that's usually not a
>problem, since the entrance end of the probe is usually shoved well over
>12" back up the tailpipe.

[EGOR's proboscus has a 22" flex nose, and an 18" straight pipe aft end]

There's quite a good graph in Heywood, of the cat's effectiveness in
"off-stoich" AFR regions (pg. 656, fig. 11-57). If you extrapolate out
those curves, you'll find that the cat is basically outta the picture
once you go much below 14AFR. It's quite surprising how fast the
conversion efficiency falls off; take a look at the graph, it was a real
eye-opener for me. I should also point out that there are at least two
other wideband AFR meter vendors (of course, both WAY more spendy than
EGOR :) that I know of that provide this same sort of probe accessory
for convenience and non-invasive tuning of aftermarket EFI controllers.

Obviously, you don't HAVE to use a probe; you can mount the Honda/NTK
sensor in a suitable place before the cat, and tune your open-loop
fueling. With the conventional switch-type O2 sensor removed (assuming
you have only one O2 bung available), you won't be going into
closed-loop anyway. If you want to watch both closed-loop and open-loop,
then two bungs or a simulated switch-type output are your two options.

However, given the cost of the Honda/NTK sensors ($90+ at the best
discount), we thot to encourage people to try the probe, if their
primary usage for such a hand-held meter as the EGOR-*meter* is in
tuning. Beyond that, if someone wants to build their own full-time
custom in-dash AFR monitor, we'd recommend you use the bung mounting,
and go for an EGOR-*module*, and we'll provide you with the circuitry
examples for making either a switch-type simulator for stoich, or even a
simulator you can use to fudge the closed-loop AFR to some value other
than stoich, either for lean-burn fuel economy games at light cruise, or
experiments we've discussed onlist, of trying to keep the ECM in
closed-loop even at high power levels, since you can make the 'pretend'
stoich to land on say 12.5 during these times. Lots of fun things you
can try/build around an EGOR-module, and of course you're then not
locked into the form-factor or design of the hand-held meter.

The EGOR-meter & proboscus combo is intended for temporary hand-held
instrument type use during EFI/performance tuning, and also safety
monitoring for avoidance of any lean excursions during initial tune or
initial high-loading trials. Once that initial tune and testing is done,
you're likely going to perfect the tuning via track times rather than
religiously setting to some 'ideal' AFR, and during these times you're
mainly using the instrument to guard against screw-ups (unexpected lean
excursions) while you tweak to optimum via track times.

If you're building a permanent installation of the sensor, either
because you're building a closed-loop engine controller, or because you
want to have full-time in-dash AFR monitoring and aren't worried about
wearNtear on a $100 sensor, then you'd probly be happier starting with
an EGOR-module, and having the flexibility of planning the display setup
and install yourself anyway. We'll be packaging and offering the
bar-graph and display portions separately in modular form, for those who
want to build up multi-channel instruments (e.g. a rack-mounted
multi-channel AFR monitor for dyno use), so perhaps those will help.

The EGOR-modules are small enough and will be affordable enough that you
can also put together several of them for "headless" (i.e., no display)
multi-channel telemetry or data-logging, if you're in a race environment
where it doesn't make sense for the driver tryna watch the AFR himself
(e.g., he's too busy to scan alot of guages), and you'd rather telemeter
that data back to your crew in the pits, or record it for later review.
That way you don't have to pay for the displays and packaging overhead
of a hand-held instrument, especially if you need many channels, nor
suffer the aggrevation of trying to figure out how to lash the hand-held
meter down to your dash, if it's a permanent, well-integrated in-dash
install you want.

Hope that answers some questions.

Gar


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