You guys are fast to give up!, the little crappy tiny plastic under the nose of VN/P Commodores certainly buggers your fuel economy when you remove it and makes it run hotter, the more extensive version in the VR/S (which also fits on the VN/VP) cuts an even smoother line through the air. Even on these big 4-5 litre cars it makes a difference. There's a guy I know that built a full car under tray for his statesman and along with other aero mods he shaved 2 litres per km out of that. He would often return 7l/100 in a 5l statesman converted to T5 manual + aero mods.
If you can get one of these factory made for a fiesta I'm on it
