Why You Should Never Lug Your Engine (Especially Turbos)

How To Destroy A Turbocharged Engine - Lugging and LSPI.

Lugging your engine, or driving at full throttle in a high gear with low RPM, can result in damage to your engine, especially for small turbocharged engines, known as low speed pre-ignition.

By accelerating in a high gear at a low engine RPM, you're putting your engine at a huge gearing disadvantage. This means the engine has to work harder, in other words in a less efficient manner. Less efficient means more heat, and the cylinder temperatures rise. When temperatures rise inside of the cylinders, unpredictable timing can occur (ping, knock, pre-ignition). Knock and pre-ignition can cause piston slap, damaging the walls of the cylinder and creating an engine that burns more oil and makes less power.

For small turbocharged engines, lugging the engine can cause low-speed pre-ignition (LSPI). LSPI is a when you have pre-ignition of your air fuel mixture (before your spark ignites it) and is becoming a more common phenomenon with small turbocharged engines running at low engine speeds with high load. It’s a dangerous condition that can cause engine damage, such as broken spark plugs or cracked pistons, as a result of extremely high pressures which occur due to significantly advanced ignition timing. It’s also very challenging to detect, and can’t be avoided through ignition timing or changing the spark plug’s heat range.

According to SubaruWRXFan, LSPI is often blamed for failures in Ford's EcoBoost engines. Apparently Ford's tune introduces a lot of boost early in the rev-range, and aftermarket tuners have pushed the boost into the higher RPM range to keep the engines safe from pre-ignition. Based on the research provided in this video, getting into boost later on is a good way of mitigating the risk of LSPI.