The Bavarian automaker’s North American arm is introducing two power kits for the BMW 135i and 335i. These kits come in two stages and can be retrofitted via the Port Installation Program at BMW centers.
The first kit costs 599 USD and consists of optimised engine software that can be applied on all model year 135i and 335i vehicles, but also on X6 models produced up to April 2010. This first stage kit enables a 20 horsepower increase in power, meaning the new output will be 320 HP and 332 lb-ft of torque (on the automatic versions) or 317 lb-ft (on the DCT equipped or manual variants).
According to BMW these extra horses will allow the 335i to become 0.2 seconds faster when sprinting from nought to 60 mph and 0.5 seconds faster when accelerating from 50 mph to 75 mph.
As for the second power kit, which carries a price tag of 1,199 USD and offers the same engine performance as the first kit, it includes an auxiliary water cooler and an new radiator fan that helps reduce the engine’s higher thermal stresses.

Source: BMW