Mention the words “retuned ECU” to most manufacturers, and they’ll void your powertrain warranty faster than you can say the world “reflash.” BMW, on the other hand, wants to capitalize on the demand for additional horsepower among enthusiast customers, so the company is offering two “Power Kits” for owners of the BMW 135i and 335i.

The Version 1 Power Kit is simply an ECU reflash that boosts horsepower from 300 to 320, while raising torque to 317 foot-pounds with a manual or DCT transmission, or 332 ft.-lb. with an automatic transmission. That matches the output of the previously announced "335i Performance Edition Kit," which was available to 335i owners only. The new Version 1 Power Kit kit may be dealer installed or port installed on a new car, and the price before labor charges is $599.

Stepping up to the Version 2 Power Kit won’t get you any more horsepower or torque, but it will get you an auxiliary water cooler and an enhanced cooling fan to cope with the engine’s added power. Version 1 is probably fine for street use, but those who regularly run track days in their cars will want to step up to Version 2, which starts from $1,199 excluding installation.

Both kits can be retrofitted to existing 135i and 335i models, or added to the option list for a new vehicle build. Modified vehicles retain the original emission certification, BMW limited warranty and fuel economy ratings, but BMW recommends installation only on vehicles that already have option code S840 (higher top speed, additional oil cooler) installed.