Green- The FX850 is true rated at 27 HP. The old J1940 system rated it 31, which meant it only had to be within 15% of the label's rated power, and was basically gross HP without an air filter or muffler where the engine had no restriction or load against it. That is the engine in my Z950. It has plenty of power for a 60" deck, and I wouldn't hesitate using one with a 72" deck on my machine unless I had a field of 3' tall grass to mow regularly. The 72" deck is offerd by Deere on a Z950 BTW.