Just a heads up. I have an intake on my A90 and Summit Racing sent me the wrong K&N filter (they sent me a stubby like that) and I was headed to the dyno the next day so I had to run it. I did a pull with the stubby and a back to back pull with the stock intake and it gained 6whp with the stock airbox. Sometimes there is just not enough surface area to flow the amount of air the turbo needs. This was also with the stock turbo and you could imagine how much more bigger singles need. I'm not saying anything bad about those in the link but just wanted to share my experience. It is now returned and I have the correct one installed.We use these to fit big singles in the n54 world:
https://docrace.com/products/n54-n55-shorty-air-filter