FUBU,

European gas isn't actually higher octane than American gas.

Read Octane rating - Wikipedia, the free encyclopedia - in Europe, you just measure the octane differently (RON vs AKI).

Your "95 octane" is our "91 octane" and your "98 octane" is our "93 octane premium."

Anyway, yes, Eurocharged do reprogram your ECU when they flash it - Eurocharged essentially overwrite your ECU's software with a version with modified flags (speed limit, etc) and data tables (mixtures and so on), while Rudy uses the Mercedes diagnostic tools in developer mode to talk to the software running on your ECU and tell it to do things like clear the VIN programming and model type (Mercedes tools in developer mode also allow the removal of the speed limiter, but I don't think they allow for the in-depth data table modification that Eurocharged have achieved, although I'm not positive and I suspect Rudy probably knows something about that too).