Here is a link to an engine being fit into an Arrow. The picture is black and white, but the exhaust just looks like alloy that is "Smokey".
http://www.avroarrow.org/interactive/irfit.asp
I'd probably spray it flat black and then dry brush the aluminum highlights. Finish up with some flat finish.
Also, as maddafinga said, the metalizers would be a good choice, but that picture doesn't show the exhaust as a single colid color so it might take a little work to get it to look "Real".