I know it's a very old post, but I just picked up an xm 14 163 and since I now have a lift and scale thought I'd post.
I compared a 08 xp, 154, with a light weight can and pretty much everything else stock.
The xm is completely stock.
Both were topped off with gas, but the xm only had 1/4 of oIL on it, so I am addin 4 pounds.
The xm came in at a WHOPPING 60 pounds more.
The scale is spot on, compared it to a bathroom scale and weighing myself.
Xp came in at 526, the xm at 582, plus 4 pounds for oil, so 586#.
163 vs. 154 = more weight.
ETEC vs. PTEK engine = more weight.
I wonder where the rest comes from?