This is what a performance air filter on ebay promises..
** Green Filters Performance Replacement Elements simply drop into the original airbox, replacing the original restrictive paper air filter with a performance, high flow element. No other modifications, parts or accessories are required. **
The pleated green cotton and mesh gauze filters have been designed to improve air flow and horsepower, offering a crisper throttle response and superior performance for improved acceleration and greater driving enjoyment. All this with the highest level of filtration, giving the ultimate protection for the engine. With improved efficiency and less restriction on the airflow, you can also see improved mpg figures, possibly giving important savings on fuel.
Can it really be that simple to get such effects on the engine? Do they deliver what they promise? Anybody tired them?