EGT

[Tom Cloud]

>> > And of course once you're off the dyno you have no feedback loop at
>> >all, which makes the EGT look even better.  At least it's telling you
>> >*something* without hauling the motor out of the car.
>> 
>> so Dave, how do you use your EGT?  If you can't actively vary
>> your fuel ratio seems t'me all you've got is a temperature.
>> You need to know the peak (which means varying the mixture
>> until temp peaks).  Elsewise, how is it of any value?
>
>Seems to me you could use it under controlled conditions of less than 
>WOT to determine such things as cruise mixture and if the probes only 
>cost $30-40 then you could put them on all 8 cylinders and really 
>have fun.  A dyno, after all, simply duplicates road conditions in a 
>lab.  Put the lab in the bronco and take it out on the road.  If you 
>really need to know WOT then get a friend's camper trailer or hook on 
>to the kid's school bus RV, take it to a good hill and run it WOT for 
>as far as you can while a navigator takes notes.  What happened to 
>all the shade tree?

I still don't know what you expect to see.  In a plane, you
peak the temp (stoich) and then lower it a certain number of
degrees to the rich side (that'd be max power).  If you did
that in a car (and I *can* do that with the ProJection),
the mixture would change the instant the operating condition
changed.  The actual value of the temperature means little
(seems t'me) -- it's the amount you're off the peak, and the
peak temp will change with varying operating conditions, so
setting the EGT for some particular temp is meaningless.  Now,
with the EGO, I *always* know that stoich is ~.5 volts and
anything higher is rich and lower is lean.  I don't know how much,
but you can't tell it with the EGT either -- esp since the
peak (stoich) temp is varying.  I can watch the EGO and know
*something*.  And once I've read my plugs a few times, I'll
have a baseline to reference (for off stoich) and I'll
always know where stoich is, if I want to tune for that.

Tom Cloud <cloud at peaches.ph.utexas.edu>