Chips are found in 1986-1995 BMW computers – roughly from E24 to E36 models. The chip is a computer EPROM located on a plug inside the engine computer (ECU). Chips contain the software that manages engine operation. Within the thousands or millions of lines of computer code are instructions and data that tell the engine how much fuel to use, when to fire the spark plugs, when and how much to change the camshaft timing, what idle speed to use, and a whole lot more. All of this data is contained in something we call “maps”. By altering the values in these maps we change how the engine performs. Make the right changes and the engine just works better – whether it makes more power, runs smoother, or gets better fuel economy.
BMW chips make big gains on 1980s-1990s BMWs because of the fuel that was available at the time. Since the stock computer lacked the ability to self-adjust, as on later models, BMW had to set the tuning for low quality fuel. Performance chips, on the other hand, have revised settings for premium fuel (91+ octane). With higher grades, the engine tuning can be more aggressive; we can run more ignition timing and alter fuel delivery to make more power before the engine experiences “detonation” (don’t worry – in most cases this does not mean the engine is exploding).
A Performance Chip is one that has the data altered, usually to make more power and torque or to account for a specific hardware change to the engine spec (cams, higher compression, bigger fuel injectors, etc). The quality of the tuning depends on the experience level of the person making the changes. Not just anyone can open up the code and make safe, meaningful changes. The best tuners are computer hackers and engine builders who know a) how to crack and modify the computer code, and b) how to tune the engine to make more power without adverse affects. And it helps to be an expert in the particular vehicle you’re tuning. Generally speaking, a tuner that can modify a BMW is not going to have the same success with a Chevy. Therefore, the most important consideration when buying a performance chip is the reputation of the tuner.