re:
"the magic 14.7 to 1 ratio"
Let me guess; your friend is an electrical engineer ;)
You'll get more power and a cooler-running engine at something richer
than a stoichiometric mixture (less power and cooler-running at a little
leaner than stoichiometric, but probably not advisable due to uneven
fuel distribution in the cylinders). I think most modern, EFI engines run a
little lean of stoichiometric, both for mileage and emissions reasons.
Bear in mind you won't get the "magic" in all cylinders--another reason to
run a little rich of peak EGT (stoichiometric)--unless you're running
multi-port,
electronically-controlled fuel injection, and a tuned input manifold, but this
would
allow you to get the mixtures pretty well balanced. A sensor in each downpipe
will
effectively "average" the readings for the cylinders in each bank. You'd want
to
couple your mixture tweaks with a dyno run to get the most benefit.
You could also do this with exhaust gas temperature (EGT) probes (essentially
thermocouples) and gauges.
I'm willing to bet you can get (nearly) as good results using the tried-and-true
"piston-pin lifting method" recommended in all the manuals (plus "reading the
plugs").
The real value of O2 sensors is in a closed-loop, computer-controlled system
where
the ECU can make instantaneous, slight and monitored changes to the fuel
delivery in each
cylinder--not to mention timing changes--to adapt to changes in fuel, air
density, load, etc.
Frankly, I think your friend's main benefit in using O2 sensors is bragging
rights.
BTW, since you'll probably run a little richer than stoichiometric--especially
if you want the most power--you'll probably be changing the O2 sensors
fairly often. Also, the downpipes are fairly thin metal so plan on welding
threaded
bosses into them to hold the sensors.
bs
********************************************
Bob Spidell San Jose, CA bspidell@pacbell.net
'67 Austin-Healey 3000 '56 Austin-Healey 100M
********************************************
----- Original Message -----
From: "Neil McDonald" <nimcdonald@shaw.ca>
To: "Healey List" <healeys@autox.team.net>
Sent: Sunday, June 20, 2004 9:28 AM
Subject: Oxygen Sensors
> In the near future I have to install a set of new headers on my BN6. With a
> minimal investment of effort or money I could also install an oxygen sensor in
> each down-pipe and use them to fine tune the mixture - targeting the magic
> 14.7 to 1 ratio. I have a friend who did this on his MGA and he swears by it.
>
> The sensors have to be mounted close to the engine in order to keep the
> operating temperature high and, in theory, they should measure around 600mv
> when the air/fuel ratio is set just right.
>
> Any one tried this?
>
> Neil
> ...........................................................
> Neil McDonald
> North Vancouver BC
> Canada
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