Barry Gardner wrote:

snips..

[As a side note, I read Tracy's earlier comment that fuel/air
mixture ratio measured by an O2 sensor was faster to react than
an EGT. This might be true but hot rodders working on chassis
dynos will tell you that the ordinary O2 sensor, while fast,
isn't accurate enough for tuning and that they prefer EGTs. There
is a special wide-band O2 sensor that is both fast and accurate
but it also costs $$$$. Before going too far down the road built
upon the ordinary O2 sensor, one might investigate this question.
If Brian Cain and John Vitamas are still on this list, they may
be able to add something to this discussion.]

John.P.Vitamvas@jci.com wrote:

Regarding O2 sensor resolution - I will reiterate my stance on this.  A
factory O2 sensor is useful for monitoring mixtures at or near stoich,
which is why it is used for emissions purposes (and fuel economy).  You
will note that no manufacturer (except Honda with their newer wideband O2)
references the O2 sensor during any condition other than cruise.  The
reason is that the resolution is just not good enough.

Now, this is not to say that it doesn't have its uses at full throttle -
you can see gross inadquacies in the fuel system with it.  That is if the
A/F ratio drops to at or near the stoichiometric level.  As most rotary
hot-rodders know, however, if you get near stoich you'd better get off the
throttle, especially in a forced induction engine.

IMHO an EGT provides a much more useful measure of relative mixture because
generally if a system is inadequate (fuel flow or injector pulsewidth too
low to provide a given power level) one will see a gradual rise of the EGT
as the mixture leans out.  This is a sign that something is amiss and that
action should be taken.  Here the slow response of the EGT is a moot point
because the entire process is slower than the EGT.

Apologies for my long-windedness.

John Vitamvas
87 Streetported RX-7 Turbo (Doesn't fly worth a darn)

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