Avoiding pre‑ignition: Why downshifting matters for engine health

Ignorance, carelessness, or simple laziness are the main reasons for one of the most common mistakes made during acceleration. Pressing the gas pedal to the floor without downshifting first is ineffective and harmful to the engine. We explain why this happens.

When drivers are learning to drive, they are informed that before performing an overtaking maneuver, they should downshift. A lower gear provides more power and torque, which translates to better acceleration and a safer maneuver execution. Nowadays, turbocharged engines generate more power at lower revs. Therefore, on empty roads with good visibility, drivers often just press the gas pedal without downshifting, which is incorrect.

A combustion engine is not efficient at low revs. The acceleration process takes longer, and energy losses are greater. But that's not the end of the problems – Japanese companies Toyota and Denso have noticed that such acceleration can lead to pre-ignition. What does this mean?

In such conditions, flammable oil and fuel particles can accumulate in the combustion chamber, which are not expelled with the exhaust gases. They glow in the chamber, and during the next compression, they ignite the mixture before the spark plug does. Studies have shown that the higher the revs, the lower the likelihood of pre-ignition. That's why it's sometimes worth "blowing out" the engine at higher revs.

Pre-ignition of the mixture results in enormous stresses in the power unit. In the best-case scenario, this can lead to spark plug damage; in the worst-case scenario, it can lead to piston cracks, rod damage, and the need for a major engine overhaul.