I'm bringing this back to the top because I was reading some stuff about engines and came across some interesting info.
The LS7 (7 liters/427ci) weighs in at
458lbs and makes 505hp, 470lbs-ft.*
LS2 (6 liters/ 368ci) weighs in at
448lbs and makes 400hp/lbs-ft.*
LS3 (6.2 liters/ 376ci) weighs in at
430lbs and makes 430hp/424lbs-ft.*
The BMW M5 V10 (S85) weighs in at
528lbsand 507hp/383lbs-ft.
BMW S62 v8 (old M5) weighs in at
526lbs. 400/369lbs-ft.
BMW s65 V8, derived from M5 v10, for the new M3 is
445lbs420hp/295lbs-ft.
BMW S54 I6 (E46 M3/Euro E36 M3) 3.2L weighs
478 338hp/269lbs-ft
Mercedes 6.3 Liter AMG V8 weighs in at
438lbs 510hp/464lbs-ft.
Audi A6 4.2 V8 weighs
422lbs 350hp/324lbs-ft. (apparently this also works for the RS4 4.2, but this is unconfirmed)
Audi 5.2L V10 weighs 484lbs 429hp/400lbs-ft
Bugatti Veyron W16 8.0liter TT 880lbs 1001hp/921lbs-ft.
VW 2.8 V6 FSI 363lbs 210hp/206lbs-ft
VW 3.2L V6 FSI 372lbs 260hp
Jaguar AJ-v8 4.0L weighs
441lbs 294hp/280lbs-ft. This is the non supercharged engine.
Toyota 1zz-fe /2zz-ge 1.8L (celica/ Lotus Elise)
225lbs (1zz)140hp/125lb-ft, and (for 2zz) 180-190hp /133lb-ft
*Jan '06 issue of Sports Car International
Italicized are quoted from Wikipedia, I was to lazy to dig through the sources.
I had a shit load of trouble finding accurate info on Japanese engines weights. Everyone either wanted to include partially assembled engines or worse, entire transmissions (RB25DEt for instance is 720lbs with it's trans, the KA24 with trans is 550).