Lighting and Heat Questions

I am using a 400mh in a 4x4 grow tent now.I have 9 plants in 3 gallon pots going,using fim and LST methods.I want to get more light so my buddy gave me another 400 watt HPS.Temps run about 77 but as soon as I started the other light they went up to 85 before i shut it off,I really want to flower with 2 400 hps.Question has anyone else ever done this and what are max high temps,any other suggestion would help,I am running two box fans outside blowing in

Turn one of those box fans around so it's blowing out. You want air going THROUGH the tent. With all your fans blowing in, you're just inflating the tent. 2 400 watts in a 4 X 4 is a fair amount of heat. Do you have air cooled hoods? Air cooled hoods, vented to the outside, and moderate air circulation through the tent should be enough. If you can't vent the hoods to the outside, the whole room is going to heat up over time. I have 2 600 watts in a 4 X 8 tent. The hoods are vented to the outside. The tent is sealed and air conditioned, with co2. I'm in the deep south where it's hot and humid. I have no temp problems at all.
Above 85, plant growth slows dramatically. Above 95, all growth has halted. You want your temps below 85, 75 is ideal. With co2 added, you can grow at 90-95, or so I've heard.

whatsup slo, red is right you want proper air flow through the tent for in-fresh new air and out-old air. If you plan to vent a tent with 2 400 watts you will want to get a squirrell cage fan or some kind of higher power fan that will keepthe air flow good and cool. A general rule of thumb I use is you want the amount of airflow to be triple the volume of your tent. My tent is 4x4x8 thats 128. 128 x 3= 384 or around a 400 cfm fan....On another note whatsup red LSU is coming to fuck yall up, honey badger era TM7!