As far as the discussion goes on this subject the fact that O2 senors can't
be used with leaded racing gas is correct. The lead imbeds itself on the
dielectric preventing the oxygen to even reach the senor itself. Even if
you run un-leaded gas the optimum air to feul mixture for an engine to make
peak performance is about 12 to 1. The O2 sensor is set up to read air to
fuel ratios of 14 to 1. This being the senors base mark it only reads
slight deviation from 14:1, say maybe 14.7:1 or 13.8:1. Also it only can
read that the mixture is richer or leaner than 14:1 and doesn't read by how
much acurately.
Exhaust temps is the way to go, but if you are going to do it there
should be one on each cylinder. That way if the is a problem with one
cylinder and not the others it can be detected. As far as getting som good
correlation numbers there must be some testing, because each engine is
going to run at a slightly different exhaust temp. There is a range of
temps that it should be running, but this wont take into account engines of
diffent compression ratio, chamber design, or volumetric efficiency. I
beleive I have those numbers on exhaust temp averages, but I'll have to dig
them up.
As far as testing goes for the proper jet size, barametric pressure
needs to be accounted for. This will affect how dense the air is with
water affecting the chamber air charge. The test should be done with an
Exhaust gas analizer, perferably a four gas version. This will read Oxygen
level, Carbon monoxide, hydrocarbons, and Nox. A five gas analyzer will
also tell CO2 levels.
This way you can get an acurate feel for unburned fuel...i.e. fuel ratio.
I also have a chart somewhere on CO and HC level to calculate air to fuel
ratios.
If this testing is done it should be at the opperating speeds of
the vehicle. This means it will have to be done on a chassis dyno,
something not avalible to most of us, but with the analizers data we can
get an idea.
The figures I have on this I am able to find. If anyone is
interested, or has any other questions please let me know.
Reuben Gosewisch
gah9@ic.mankato.mn.us
Automotive Engineering Technology major Mankato State University.
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