Another Engine

Yesterday Creativelenna gave us a little quiz - to identify an object. I was very proud to know it was an engine, and a V12 at that. Then quite by chance I spotted this one on blip patrol today, so just had to put it up.
Do you know what sort it is? I confess I had no idea (except for the 6 cylinders) so had to ask the mechanic, who incidentally admitted to being this artist.
Answer below:

Part of an RB25 inline 6 cylinder 2.5L engine from a Nissan Skyline. John says it is 'from a hot car' - something to do with the number of valves per cylinder I believe, but that's enough technical detail for me.