The machining (and the fact it has four valves per cylinder) makes me think it's from something more modern than a straight 8. Perhaps one of the prototype V16 that BMW was originally going to shove in the Phantom?
Inline 8 - W196 Formula One racing car, or the 300SLR sports racing car?
V16 - The BMW Goldfish V16 trialled in the new Bentley Mulsanne in the early 1990s or one of the Rolls-Royce Phantom Coupés which featured in the film Johnny English Reborn is powered by this V16 engine.