How are you calibrating / adjusting for water injection AFR?

[Forum Admin]

An EGT reading will tell you that you are in a dangerous state - but it doesn't tell you why. It could be timing or fuel ratio.

AFR readings from anything other than a wide band lambda sensor is pretty much uselsess. When people talk about monitoring AFR for engine tune - it should be with a calibrated wide band limbda sensor.

A wide band lamda sensor measures partial pressures in the exhaust to interpret the components of your induction charge. Unlike O2 sensors which are only accurate around a very narrow range near stoic a good wide band lambda can provide you with your AFR from 10:1 to leaner than 20:1 - if it has been calibrated for your fuel inputs (i.e. gasoline, methanol, propane, etc.) and has been calibrated for any water injection rate (since water injection dilutes the partial pressures and apparently tends to cause readings closer to stoich than truly exist).

In knock limited tuning situations, most setups have known AFR limits. For instance a given engine may run fine at 20psi and 11.25 AFR at MBT with 93 octane, but need to be at 11.00 AFR with 91 octane and 10.50 AFR with 89 octane. This is why many prefer to tune by AFR - the target is known from many uses. Once you are at the target AFR the tuner is able to tune to MBT. This becomes the "preferrred" tuning and monitoring tool for tuners that want to run at MBT and use fueling levels to suppress knock.

Yes if you run past MBT you will get knock at appropriate AFR levels even rich AFR levels.

With water injection and other knock suppressing technologies AFR no longer becomes a target - but a result. Without knock limits you can tune for maximum AFR power - using either a dyno or cylinder pressures. Then you can advance from there to MBT.

There is no single best monitoring tool. EGT is a quick check if everything is OK, but will not tell you what exactly is out of tune fuel or timing. AFR is good only if you know what your AFR is supposed to be for the components your charge mixture in the cylinder (including correct octane) and the sensor is calibrated for your charge mixtures. To the extent possible good quality knock monitoring with timing retard will protect your engine - but does not necessarily resolve a bad tune.