Originally Posted by cryo

Think of it this way, the stock tune will fight you when it comes to trying to make the engine "flow better" and will actually result in very similar performance while taking the engine far away from its safe zone. The stock tune is calibrated to hit specific load values as well as boost values. As soon as those variables become uncontrollable so does the life expectency of the motor.

An aftermarket tune actually makes the computer take advantage of the modifications and works with them rather than against them.

Hope this helps.

Dave