...mark my words...
The engine they'll use will not have the same output as any other engine out there right now. It *may* share a name...but it will be a modified version of something they are using right now.
It's just a feeling I have based on a year and a half of speculation.
EDIT: I am curious, though...based on comments like the one below - what engine are we talking about? The 'base' V8? or the monster?