Learn how LSPI affects your engine and how to carefully choose the right engine oil with the LSPI Impact app.
This app is optimized for the iPad but also works on any other iOS device. LIQUI MOLY: LSPI Impact is available in English and helps to explain Low Speed Pre-Ignition
LSPI (= Low Speed Pre-Ignition) or SPI (Stochastic Pre-Ignition) describes the unwanted pre-ignition that occurs stochastically in the combustion chamber. It occurs at high load and low engine speed in turbocharged engines with direct injection before the spark plugs begin to spark.
This problem is caused by the downsizing of engines, which means that modern engines have less displacement but are still supposed to deliver the same or even greater power.
The cause of LSPI probably lies in the motor oil, tiny quantities of which get into the combustion chamber, where they are ignited in the compression process. The combustion flashes over to the fuel/air mixture and results in heavy engine knocking.
Carbon deposits are also considered a significant factor in LSPI. Modern, direct injection turbocharged gasoline engines have a highly stressed injection system. The injection nozzles extend directly into the combustion chamber, so they are exposed to high temperatures, pressures and the influence of combustion residues. Deposits form rapidly at the nozzle outlets. Due to the high temperatures, the particle deposits can start to glow and ignite, which can lead to engine knocking. With LSPI the pressure in the combustion chamber is about three times that for normal combustion. The extreme pressure means that massive piston damage can occur within a short space of time.