O2 Sensors

QUESTION: Do any of your books help in areas of tuning with using O2 sensors? I am needing some what of a baseline for a good tuneup using the correct nozzles, pills to help with getting the most or should I say most consistent in drag race ET’s. Of course everything being the same.

Thanks for replying, R. in Texas

Hi R in Texas,
Thanks for your inquiry. Our Jetting for Racing Mechanical Fuel Injection … book has info on O2 sensors including accuracy limits.

REPEATABILITY VS ACCURACY: O2 sensors are a great tool, however, the accuracy (especially for methanol or ethanol) and repeatability may be issues. Accuracy is less of an issue if they are repeatable. That is, regardless of whether they are accurate or not, you can rely on the reading if they are repeatable. An example would be a speedometer that is out of calibration. You learn how much it is off and drive with that error in mind. If it is jumping around from a binding drive cable, and not repeatable, then it is difficult to gage you speed.

REPEATABILITY: Regarding the repeatability of the O2 sensor method, that is a question. They respond to the condition of the exhaust. Especially if you run methanol or ethanol, I am not sure whether the instrumentation technology with those fuels is fully developed yet. You can have a rich cold exhaust gas or a rich hot exhaust from different air to fuel ratios from different tuning results and I am not sure the O2 readings would be repeatable. Another source of error would be the combination of sensor location and heat soak from prior running.

WITH SOLVENTS: Auto dealers have cautioned in the use of solvents around O2 sensors. That could affect the readings.

OEM APPLICATIONS: In the highway vehicle, O2 sensors are used as a device to steer the air to fuel ratio, not necessarily determine it. And most highway vehicle computer controls include a cold engine warm up default to get through the warm up cycle before relying on the O2 sensor. Rich mixtures of racing fuels along with sensor location may send the exhaust into that range or may not. Just a caution. In drag racing, the variability of engine temperatures is a problem. In circle racing, the engine gets up to a temperature and stays there. Not so in the drags. It starts out cold and warms up on the run. How hot it gets in the exhaust is often dependent on how long you were sitting in staging. That may effect the sensor.

AFR: Air to fuel ratio is extensively explained in our 5000 HP methanol book and also illustrated in our Fuel Injection Racing Secrets book. It is based on pounds of fuel per revolution vs pounds of air per revolution. We go to great lengths to make repeatable methods to determine air to fuel ratio.

AFR & O2 SENSORS: An O2 sensor would definitely help but I am not sure how well it works as a repeatable indicator of the air to fuel ratio as the tuning tool. Consultations with a couple of the manufacturers last year indicated they were not sure either.

All the best,
Bob Szabo