I looked at the info on the Bully Dog web site (it's linked at the top of the page- with other ads supporting this forum) and there is a lot of info. You first have to download the latest program, based on your vehicle, and update the "Power Pup". So the device itself does NOT contain data for all vehicles. Then it takes maybe 20 minutes to reprogram the ECU- NOT twenty seconds, as suggested. It can be used to change the speed limiter, the reve limit, and the idle. It will also read/clear trouble codes. To affect power, it can only change fueling and timing. No details on how much, but that would likely vary from vehicle to vehicle. With any ECU change, the timing and fueling are the most significant variables that affect power. It would be nice to have a set-up that would let you change both items by adjusting the "curve" but that would be a fancier, more expensive device, and would be risky for most people. And if anyone wanted a RWD high performance vehicle, the Infiniti and the Hyundai both offer better value than the BMW- but not the snob appeal.