overboost

It makes sense to provide plausible engine fuel and ignition mapping to the limits of the factory fuel injectors, which would typically be sized sufficiently large to provide optimal fuel to the airflow/boost limits of the stock turpocharger even though the wastegate should normally prevent the engine from boosting so high. This is because the engine can overboost if the wastegate manifold-pressure reference line is cut (melted, crushed, disconnected, and so on), and a "safe" calibration -- even in forbidden overboost territory -- is one more countermeasure designed to help avoid engine damage from lean mixtures if the engine does overboost if fuel cut strategies fail.

Manifold pressure exceeding the limit lines shown in figure 5-2, constitutes an overboost.