Timmmm, i found driving at 90KPH with CC set gave me 4.4L/100k that was over blue mountains and out to Dubbo then down golden HWy to Muswellbrook then down the putty road to windsor then to Sydney CBD just over 1,200 on the same tank for 4.4L/100k average shifting gear b4 2,000 rev useing 5th gear most of the time, if i drive at 100, 110 120 best i get is 4.9L/100k, if i excellerate a lot and drive at 110 120 its about 5.5L/100k, but when i had the scangauge and watched that it shows fuel useage as it happens i could get better economy and still drive at 110 120. the sport muffler like Thumper had helped a bit too but i use stock now.
but when i drive the company 4 cyl petrol toyota it gets 12l to 14l/ 100k in sydney