Some are obviously better than others, others just 'fool' the engine into believing and/or reading sensors incorrectly which in turn give more boost/fuelling etc...
An MTM, Revo or Shark one will have been mapped properly. I’m not sure if you have an Audi warranty, Ian, but they will be able to tell you've had one of these on anyway, even if you remove it pre-service. It brings up a code, TD1, I think, which lets them know the engine was running harder/hotter or faster than OEM specs even if you've removed the box.
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2009 Audi RS 6 Saloon V10 - 420mm Ceramics, Keyless, Soft Close, Adaptive Cruise, Glass Sunroof, Blinds, Twin Pane & UV, Freeview & DAB, High Beam Assist, MTM bits, Audi Exclusive Bits, MRC, Milltek, GYEF1 ASY2's, Bluetooth streaming music to AMI mod - 753 PS/1021 NM
2016 Audi S3 Saloon, Sepang, S-Tronic - B&O, Tech Pack etc... Company Car
1995 Audi A8 4.2 V8 quattro Sport - Bose, Solar, Blinds
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