wheaty, John W told of the biggest difference - overall size. 8820 has a turbo and aftercooled 466 that is around 225 hp, has the hydraulic pump in the engine compartment. The 8820's all have the better tailings elevator and combines above SN 434651 have the big clean grain elevator. The T2's have a 6" longer shoe. Capacity wise between the 77 and 88 you are looking at around a 20% difference in capacity - ie 643 and 920 on 7720 and 843 and 925 on 8820. If you found a good 77 and don't need the extra capacity I would go with it. 95