Scot J

So what are the primary differences between the r8 and s5 4.2 v8? Compression and....??

AofC_RR

R8 has dry sump. The internals are completely different. There has been much discussion on the topic but more so on the RS4 side. If you're looking to get similar power you'd be better off buying an RS4 motor to drop in.

mdwredb7

Probably safe to say that other than the displacement, there's not alot in common...

Mcqueen

To the guy who was going to rebuild his S5 engine into an RS4 engine?

AofC_RR

And opted out. People advised buying a RS4 motor instead. Cost would probably be similiar and way more labor efficient.

rferni

I think he stated he was going the supercharger route!

RestonS5

See this post. Down the page, an RS4 owner calls out some key elements.

http://www.6speedonline.com/forums/showthread.php?t=103884

TO say the least, there are numerous internal differences in design and components.

If you want more detail, the Audi Self Study Training book on the 4.2L engine is # 921603 and can be ordered from this site.
http://www.audi.ddsltd.com/

keman

same compression ratio (12.5:1), same number of valves, same displacement, different everything else