Here’s a cold, hard fact of life that most of us try to ignore: if you reflash your car’s ECU, then swallow a valve or put a piston through your engine block, don’t expect that to be covered under your car’s warranty. In fact, any changes to your car’s ECU will generally void the powertrain warranty granted by the automaker, unless there’s some other pre-written arrangement between the automaker and the tuner. That’s not to say that mods will void your entire warranty, but if a manufacturer can prove that a failure is a direct result of modification, you’re on your own.
The best tunes, therefore, are the ones that come directly from a manufacturer. Last July, BMW offered a factory tuning program for buyers of the 2011 335i; for a very-reasonable $550 (plus installation), BMW would reflash the ECU to give you the same level of power as a 335iS. That meant a power increase from 300 horsepower to 320 hp, with a subsequent boost in torque up to 32 ft-lb (automatic transmission) or 17 ft-lb (manual or DCT transmission).
Now BMW is taking what they’ve learned and offering the same tune for owners of any year 335i, as well as any year 135i. For $599 (plus installation), BMW will sell you its Version 1 Power Kit, which consists of an ECU reflash. For those that track their cars, a Version 2 Power Kit gives you the added horsepower, plus added cooling in the form of an auxiliary water cooler and a higher flow fan.
The good news is that the kits retain all applicable BMW warranties, as well as emission certifications and stock fuel economy. The bad new is that the kits should only be installed on cars ordered with BMW’s option code S840, which includes a higher speed limit and an additional oil cooler.