We always hear people talking about ‘that heavy V8’ in the 4.2 cars when they’re scrambling for a reason to dislike the 4.2 FSI. It’s a pretty weak swipe…saying you don’t like a V8 is like saying you don’t like good food and perfect weather. Besides, the 4.2 FSI engine is made of aluminium, and the intake manifold is made of magnesium. Further, it’s a densely packed, very compact 4.2 V8. Calling it heavy seems a bit of a guess…sounds like something people say without doing their homework. So I wanted to see.
Cue the self study guide…here’s what it says: approximately 467 lbs manual transmission including clutch and dual-mass flywheel
Interesting. If I am reading that right, it’s 467 lbs + the 26 lb flywheel and the 15-20 lbs clutch (guessing on the clutch). That makes sense because the same study guide says the lower revving 4.2 FSI in the Q7 and S5 weighs 437 lbs.
So we can say the RS4 engine weighs around 430 lbs, and the S5/Q7 engine weighs 437 lbs.
http://www.s4-mtm.com/images/RS4V8-StudyGuide.pdf
To do a comparison, I thought I would have a look at the popular 3.0T. It would make sense to use this engine as a comparison because it’s the new, more efficient and apparently lighter engine, and is the next generation engine for the S5 and Q7. It’s also the engine owned by the people who throw the ‘heavy 4.2’ insult around most often 
Of course the new 8K cars aren’t really that light…they’re mostly4000 lbs or so, more than the 8E cars. I’m suspecting the 3.0T isn’t really a featherweight…
Audi says: 3.0T - 418 lbs
http://www.s4-mtm.com/images/925803_3.0V6TFSIengine.pdf
???
Wait, so the 4.2 only weighs 10-20 lbs more than the 3.0T? That’s interesting. So much for the heavy V8 talk. I guess the smaller displacement 3.0T engine has the handicap of a 50 lb supercharger in the valley, not to mention intercooling etc.
Anyway, just thought that was a neat comparison.
http://www.audiworld.com/wp-content/uploads/2007/06/header317.jpg
