btf-ford, devices that disturb the air in an intake can work on carby fuelled cars just by stopping the fuel dropping out but has never been proven to do anything injected cars. But under trays do work and always have worked, it's just matter of how much. There are entire sites/forums for guys dedicated to modifying their cars in this way and when they go to extremes with aero mods they get crazy fuel economy in old Honda Civics that make econetics look like 6 litre v8s
