overboost

To increase an engine's intake manifold pressure to higher levels than it is designed for.

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.

Morgan was waiting outside in the bay. Didn't even wait for me to say a word. "What happened? Why did you overboost? You could have blown the whole shuttle, the whole expedition."

The process of overboosting.

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.

These planes all have popoff valves, designed to prevent overboost, but the flow dynamics are such that manifold pressure can seriously overshoot redline before the popoff valve opens.

An instance of overboosting.

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

By delaying opening of the wastegate, the ECU could generate an overboost at full throttle, increasing boost pressure to 1.1bar, for a peak power delivery of 230bhp in short bursts of up to 30sec at a time.