5-wire O2 Sensor Sources

Garfield Willis garwillis at msn.com
Thu Apr 11 23:21:18 GMT 2002


On 11 Apr 2002 16:54:56 EDT, Shannen at grolen.com wrote:

>That's kinda funny, as major racing engine builders in this area don't
>even use an O2 sensor.  They measure air/fuel ratio on the  intake side
>of the engine.

You talking mostly about drag car engine builders?

That's fine on the dyno, and the old reliable way to do it before AFR sensing
came into vogue, specially when you're dealing with carbs that don't have
recirculating fuel to subtract on the return side from the delivery side
measurement (and almost the same as the return side flow). Not as accurate in
recirculating EFI systems; subtracting two big numbers from each other to find
the much smaller difference is called a "common-mode rejection ratio" problem in
instrumentation. Requires much higher resolution/dynamic range flow measurement
to get the same accuracy than with returnless.

But measuring the mass flows for air and inNout fuel at the intake is pretty
problematic doing that on the track. I don't know of anyone that does that on
the track, do you? Plus especially on carb'd cars you also wouldn't see any
mixture imbalances caused in the turns.

Many teams have long since gone to a sensor per runner, and during tuning on the
track, telemeter all that stuff back to the pit, along with a ton of other data
including suspension positioning, etc. etc.

I recall Frank Parker telling me about how the factory C5 Corvette team would
buy NTK blue boxes in lots of 8 and strap them together! As in $8k+. Ouch.

Gar

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