There is a big number of chip modules either for petrol or for diesel car available nowadays. Both types of devices mostly change supercharging rate or injection duration.

In the past, when petrol engines were normally aspirated in majority, chip-tuning affected injection duration or had to deal with ignition delay. It caused comparatively small power increase, which was in range from seven to ten percent. To achieve greater effect on atmospheric motors, there is a need to improve air intake (channels, valves, camshafts), and exhaust processes (specially designed manifold). Nowadays, when new generations of small volume supercharged petrol engines are commonly used, automobile owners have easier, safer and cheaper alternative: they just have to install additional electronic unit and get up to 20-30% power increase.

So, as you can see from the aforementioned, type of fuel does not play important part in the question discussed. The main issue is whether the engine is atmospheric or equipped with turbine, because chip-tuning shows best results when applied to the motors of second kind.