Why density matters
When the Nexus works out fueling, it first calculates how much fuel mass the engine needs for your target air-fuel ratio. Injectors, though, are rated by flow volume. To turn one into the other, the ECU divides by the fuel's density. If the density is off, every fuel calculation is off by the same proportion.
When the table is used
- Fuel Type set to Petrol, Flex Fuel or Ethanol Petrol Blend: the table is active and sets the density of the primary fuel, which is gasoline. In flex and blend setups, the density of the secondary fuel (the ethanol) is fixed in firmware.
- Fuel Type set to Ethanol or Methanol: the table isn't used. The Nexus applies the correct built-in density for that fuel automatically.
Values in Haltech firmware
| Fuel | Density used | Approx. lb per US gallon |
|---|---|---|
| Gasoline (petrol), default | 737.2 kg/m3 | 6.15 |
| E85 | 777.8 kg/m3 | 6.49 |
| Ethanol | 785.0 kg/m3 | 6.55 |
| Methanol | 791.8 kg/m3 | 6.61 |
Should you change it?
For pump gas, the default is a good starting point. If you run a race fuel, check the supplier's data sheet; most list density or specific gravity, and entering the real value keeps your fuel model honest. Changing it will shift fueling across the whole map, so re-check your AFR afterward. More on the model in Fuel System and Tuning with VE.
