Often times it is ECU engine timings. See the many ECU tune kits available for many cars.
More aggressive tunings can also be harder on the engine. Factory tunes work a bit like binning and overclocking - the higher clocked CPUs are often selected for better quality control, and lower clocked CPUs are the same part, but with less rigorous quality control (or at least they don't have to pass at the same extreme high level).
So just like you can overclock a CPU, you can often overclock an engine... but if there are mild defects in the engine block the results can be disastrous.
This also affects fuel economy, which is regulated, and also affects consumer buying decisions. So optimizing the ECU tune for performance and for fuel economy are often somewhat different optimization points. For instance, BMWs have a button for "Eco/Comfort/Sport" mode, which among other things, can sometimes change the engine timings from a button in the cabin.
Just like underclocking a GPU can get 80% of the performance for a fraction of the power, and overclocking by 10% can use 20% more power, the same is true of the ECU timings.
More aggressive tunings can also be harder on the engine. Factory tunes work a bit like binning and overclocking - the higher clocked CPUs are often selected for better quality control, and lower clocked CPUs are the same part, but with less rigorous quality control (or at least they don't have to pass at the same extreme high level).
So just like you can overclock a CPU, you can often overclock an engine... but if there are mild defects in the engine block the results can be disastrous.
This also affects fuel economy, which is regulated, and also affects consumer buying decisions. So optimizing the ECU tune for performance and for fuel economy are often somewhat different optimization points. For instance, BMWs have a button for "Eco/Comfort/Sport" mode, which among other things, can sometimes change the engine timings from a button in the cabin.
Just like underclocking a GPU can get 80% of the performance for a fraction of the power, and overclocking by 10% can use 20% more power, the same is true of the ECU timings.