Petrol and Electric Heads

[Whippet]

I found some density data from a Singapore refiner, so it probably applies here. Both 95 and 98 are listed at 724.7 kg/m3. There are variations in density for samples, but not related to the RON. That would suggest that mileage differences are a furphy.

Exactly.

Do you think if the knock varies due to the grade for a given situation that changes to the ignition timing and possibly the fueling would alter the economy?

Short answer - yes I do.

Longer answer - My understanding is that the ECU is doing this all of the time, many times a second; as there will be small variations in the actual RON between tankful’s for the same RON petrol from the same supplier but from different tanker batches. The ECU is constantly modulating ignition timing to check the onset of pinging via feedback from the knock sensor, so as to optimise the maximum achievable ignition advance in accord to the reference MAPS, to achieve maximum engine performance and economy. When the ECU is controlling the parameters that enable the engine to achieve maximum performance for a given condition, then less fuel is needed to maintain the same kW output at the flywheel. Hence the fuel consumption is optimised.

Cheers