I bought this for my 2002 BMW 325i (E46) M54 engine. Fits the stock air filter box perfectly. An air-tight fit is key to fuel-injected engines that have air flow sensors. Proper intake air flow is essential. This is a perfect OEM fit and performance is excellent. Because of the high amount of air flow the BMW engines require, a clean air filter is a must for best performance and optimum gas mileage. I let my air filter go unchecked, and wondered why my gas mileage was 15% lower, all due to a very dirty air filter!Installation is simple: Install up into the air box top, upper half of the assembly, NOT in the lower, bottom half of the box. Simply install orange foam-side down, with the filter ribs going UP into the upper, top half of the air box. Push orange foam seal into the lip evenly all the way around to ensure a secure seal when the spring clips go down. Also, make sure the air box seals down to the bottom half securely before engaging the retaining spring clips around...