Outer Limits 4x4 Board

Hi guys mates got an 08 patrol 3.0 manual wagon and has recently installed a taipan exhuast. going to towoomba range on sunday EGT'S shot up to 650 degrees. the car had no load and wasnt towing anything. ambient temp was low 20's and air was wuite crisp. any thoiughts on these seem to be high temps and what is the safe range for these motors? also the carhas the standard computer in it.

thanks.