[richs347]

On the SD cars, the computer runs off a set of pre-made fuel and timing tables. It's very limited to what it can change based on your additions. So, if you're adding heads, intake, etc... you're substantially adding more air, which needs more fuel... and the computer isn't able to compensate.

On the mass air cars, the meter reads the amount of incoming air and the computer is designed to read that amount and adjust the timing and fuel curves. The newer computers also use adaptive control and have the ability to learn and design new tables based on what it sees through the 02's in closed loop. It's a much better system to use when making modifications on the car. With a NA car, until you get to about 42 lb injectors you can just tune the car with timing and fuel pressure adjustments and the computer will usually work with you. (As long as fuel injectors are matched to the mass air meter and are the right size for the application).