what are differences between 3.0/4.8i and 3.0/4.8si?
 

I am looking to make the jump from my e53 to the e70 but I am wondering what are the differences between these models. Are they cosmetic or mechanical?

Numeric: 4.8 - 3.0 = 1.8

what year are you looking at? I ask because the 3.0si is going away.

In short, it is both cosmetic and mechanical.

Im looking for a 07 or 08. Do the SI's have flared arches? etc...

3.0si: no arches, does not come with 20" wheels, though they can be added yourself
4.8i: you need the upgraded wheel pkg to get the arches and 20" wheels

There are other cosmetic differences like the kidney grills and tailpipes. Mechanically obviously the motor. Also note the '07s might not have the moonroof as it was an option whereas it was pretty much a given on the '08s for either model. '07s didn't have auto-tailgate or auto-hold either.

thanks