BOG describes a frustrating engine response lag specifically experienced with Rotax engines, occurring when the power valve closes during braking and the throttle is then reapplied whilst engine speed remains above 7,500 RPM. This phenomenon creates a momentary hesitation or flat spot in power delivery, potentially costing valuable time during corner exit.
Understanding the BOG condition:
- Caused by the power valve's position being mismatched to throttle input
- Most noticeable when braking late and getting back on the power early
- Can be minimised through proper driving technique and power valve adjustment
- Typically lasts only a fraction of a second but feels significant
Experienced Rotax drivers learn to anticipate and work around BOG through specific driving techniques, such as slightly blipping the throttle during braking or adjusting their corner entry speed to keep the engine below the critical RPM range when back on power. The PV spring pressure adjustment (the red knob on Rotax engines) can also be tuned to reduce BOG effects, though this requires careful calibration to avoid sacrificing overall power delivery.