I believe there is about a 10-15% loss through the drivetrain to the rear wheels. Dynos have varying methods of correction so it all depends on the brand and settings. There is a nominal cost to return the ECU back to stock including the cost to ship it to us and ship it back but it is much less than the original price. We offer a free 3 time reflash on the kit so if your dealer resets the ECU and gets rid of the software, we will perform the reflash for you 3 times for free. You just cover shipping the ECU to us and shipping it back. It is 328xi compatible, we can do ANY of the engines
