If the powertrain is identical, there's not much the ECU can do.
tuning is thrown around a lot and means different things to different people.
ECU tuning is one thing, and basically you can set the ECU to run the engine more aggressively (for power and torque) or more conservatively (for fuel economy). This usually involves ignition timing and fuel injector pulses.
However, two engines with the same engine displacement, same number of cylinders and same number of valves can have different power outputs and different torques based on how they are designed.
Changing this design involves major cost and surgery, but engines are already
tuned from the factory based on the design decisions that were made. Basically:
- the length of the intake runners
- the bore and stroke ratio of the cylinders
- the length of the piston rods
- the size and length of each cylinder's exhaust piping
To change bore and stroke, you need machining, new piston heads, maybe new piston rods too.
To change piston rods, you will change the compression ratio and may need new piston heads.
Intake runners can be changed, sometimes there's the entire intake plenum of a similar engine that you can bolt on, but usually, a new part needs to be machined.
Exhaust piping is a more common bolt modification because it if physically simpler. An exhaust header would do this.
Depending what you do, it will shift the power band and torque band to higher or lower RPMs.