okay, well it all depends on which 770 you plan on getting. If you get a 770 with a cooler that directs air out the rear of the case, such as this one:
Then you will want to add a couple of fans as close to the GPU as possible, directed so that threy are removing air from the case. This is due to the cooler on this type of 770 dispersing air into the case. On average though, 4 fans arranged a 2...
If by cha you mean chassis, it depends on a whole load of factors, including what case you've got, which 770 you are buying and whether your CPU is air or water cooled.
okay, well it all depends on which 770 you plan on getting. If you get a 770 with a cooler that directs air out the rear of the case, such as this one:
Then you will want to add a couple of fans as close to the GPU as possible, directed so that threy are removing air from the case. This is due to the cooler on this type of 770 dispersing air into the case. On average though, 4 fans arranged a 2 fan push, 2 fan pull arrangment should do the trick. =)