I think there is more to the EP than just the "Extended Drain Interval" aspect of it. I think the chemistry itself is totally different. When I emailed Mobil about the EP for my Modified Lancer Evolution, and that I was changing the EP oil every 3K miles, they responded by saying that was a good idea, and the Oil will hold up well in my application due to added friction fighters, more SuperSyn, and more cleaning agents. Extended Drain Intervals in High Performance Vehicles is not a good idea in my book. These type of cars just beat the [censored] out of oil. I still think that "supersyn" is just Group 5 basestocks. No one will ever really know. haha.