S4 4.2 v.s. A6 4.2 Engine?

[Dan255]

I've heard that the 2.7t A6 and S4 engines are the same, but are the 4.2s? I have an 04 A6 4.2 parts car, and I was wondering if it would be possible to swap that into an S4 that has a tensioner failure? I think I remember hearing that they are different, but my searches didn't come up with any definitive answers. Sorry if this question has been asked before, but I appreciate any response. Thanks, Dan.

[JimmyBones]

The 2004 A6 4.2 engine is the old timing belt engine. The C5 V8 Allroad and 2005/2006 C6 A6 V8 is the same as the B6/7 S4 4.2 V8.