My daughter's QX50 with the VC turbo engine gets pre-ignition on regular and medium grade gas, but it's fine on premium. I've had a few cars over the years where premium is recommended, but they have always run regular with no problems. My understanding of what happens is the spark advance is somewhat reduced if the knock sensor "hears" any knocking. And this happens before a human driver can hear it. I told her to ask the dealer about it at her next oil change, but I'm wondering if this engine is somehow different than other high-compression engines that run just fine on regular gas.