I fitted this on my BMW 328i SE and the BHP I get from it 8 BHP increase on my 328i now I checked the fitting and it fits fine on my S4 but I don't if it gives me any power
X-1 intake from the states is the best I could find, really shields the heat wheel from the filter, anything else the stock box really is best. Expensive though, and comes from the US, all carbon though, think MRC get em in sometimes too.