I never compared weight between the 03 4.6 to the 351W that I removed from the car. I was told that the 4.6 was roughly 85lbs heavier. Granted the 351W had aluminum heads and intake, the 4.6 felt alot heavier moving it around and setting it in the car for mockup. I wish I had weighed them for a comparison. Which mine is a iron block compared to the teksid aluminum.