The Volvo Penta web site has an on line parts list.
http://www.volvopentastore.com/Engine-P ... ore_id.366 Looking at engines from about 2002 as a sample, the 320 hp 5.7 GXi uses roller rocker arms where the 280hp 5.7Gi does not. According to the parts lists I looked at, the crank, cam, heads, pistons, etc. are the same. In about 2008 -2009 Volvo changed the horsepower rating of the 5.7 Gi from 280 to 300hp while using the same standard rockers. I have heard that some people felt the 280 hp was a conservative rating. Starting around that same time, the 320hp 5.7 GXi max rpm also went from 5000 rpm to 5200 rpm. The 5.7 Gi max rpm remains at 5000. These engines are all multi-port fuel injection. I am not sure what tuning changes have been made in the engine's computer.