Originally Posted By: A_Harman
The cause of LSPI is more than theory. I saw a high-speed combustion research film of an LSPI event not too long ago. It showed an oil droplet wafting across the screen, and then all of a sudden the whole screen lit up when the whole cylinder charge went off at once. The oil droplet was the ignition source for the whole event; the spark plug never had a chance to fire. LSPI is more of a concern on downsized turbocharged engines in heavy vehicles. Something like the 1.5L turbo in the Malibu, where the engine can be lugged at 1300 rpm under full boost. I don't think DI by itself is the cause of LSPI, it's more likely the result of higher compression ratios that are built into DI gasoline engines. DI done right, such as in a stratified charge combustion mode would not have explosive end gases, and would not be subject to such volcanic explosions.
As long as you aren't lugging your WRX at full boost under 2500 rpm, I don't think LSPI is much of a concern. I think that the high-performance nature of the car, sort of minimizes that concern all by itself. But in general, I think characteristics of oils that would make them less likely to contribute to LSPI is to have low-SAPS to minimize Ca, full synthetic to maintain a tight distribution of base stock molecular weights, and low volatility to minimize the presence of oil in the combustion chamber. I think M1 ESP 5w30 would be a good example of this kind of oil. Owing to the low SAPS, oil change intervals would have to be short, such as 5k miles, max.
It sounds like a quality air/oil separator and/or atmospheric venting of crankcase gasses could go a long ways with respect to LSPI.
The cause of LSPI is more than theory. I saw a high-speed combustion research film of an LSPI event not too long ago. It showed an oil droplet wafting across the screen, and then all of a sudden the whole screen lit up when the whole cylinder charge went off at once. The oil droplet was the ignition source for the whole event; the spark plug never had a chance to fire. LSPI is more of a concern on downsized turbocharged engines in heavy vehicles. Something like the 1.5L turbo in the Malibu, where the engine can be lugged at 1300 rpm under full boost. I don't think DI by itself is the cause of LSPI, it's more likely the result of higher compression ratios that are built into DI gasoline engines. DI done right, such as in a stratified charge combustion mode would not have explosive end gases, and would not be subject to such volcanic explosions.
As long as you aren't lugging your WRX at full boost under 2500 rpm, I don't think LSPI is much of a concern. I think that the high-performance nature of the car, sort of minimizes that concern all by itself. But in general, I think characteristics of oils that would make them less likely to contribute to LSPI is to have low-SAPS to minimize Ca, full synthetic to maintain a tight distribution of base stock molecular weights, and low volatility to minimize the presence of oil in the combustion chamber. I think M1 ESP 5w30 would be a good example of this kind of oil. Owing to the low SAPS, oil change intervals would have to be short, such as 5k miles, max.
It sounds like a quality air/oil separator and/or atmospheric venting of crankcase gasses could go a long ways with respect to LSPI.
Last edited:
