Between 70% to 100% throttle and shift between 1,800 - 2,500 rpm.
There is an article on
www.autospeed.com that tests this I just can't place my finger on it right now. I'll edit it in if I can find it.
Edit: Found it!
Brake Specific Fuel Consumption
http://www.autospeed.com/cms/A_110216/article.html