Can you guys educate me on after market air filters.
Can you put on any air filter that fits???
I'm talking about like a K&N cone filter???

There reason I ask is i've got one from my brothers toyota corolla H plate just wondered can I just put it on mine as it fits on just wanted to ask 1st.

If I can then why do all these manufacturers sell them for specific cars especially when their cone filters and most are all the same size cone.

Forgive me if i'm being stupid

As long as the diametre of the filter at attachment fits over or in the air intake part where the filter fits on then its ok.

Brilliant as I think the K&N will be louder and make a nice grunty noise incomparioson to the non-branded hks look-a-like I've got at the minute.

yes the only differance is the dim as thecopper has said. You can if it dont fit get a piece of plastic/metal pipe to make up the wall thinkness so it does...(if its too big that is LOL)

That is true - it is also different on the neck of the filter .. i.e. some are angled across and down so they fit in the engine bay ok, also got to think about the brackets - these can be home made tho, thats basically all the differences