Hello, I read a few weeks ago that there are problems with Audi vehicles (perhaps also with other brands) with the effectiveness of the filter in practice. The problem seems to be the necessary operating temperature of the filter in order to become effective at all. Wouldn’t want to say more about it. To start the topic: Who of you has already retrofitted? Does the filter have the effectiveness promised by the individual manufacturers? he filters suitable for chip-tuned A2, or are there certain limitations, such as loss of power etc.? Let my questions be neutral here. The discussion should become factual and remain. I greet you