My 2 cents worth... I went for a car cruise today. Mixed drive of straights and winding roads. We drove about 350kms, got 8.0l/100kms. I use BP Ultimate 98, a KN panel filter, I've changed the rear exhaust mufflers and I use 225/45 18" tyres. Also, a lot has to do with your driving... releasing the accelerator long before it's time to brake might help.