-3 to +3

It's nothing near what they say it is.

Remember a CAI will help an engine get more air... but if it's the same engine and exaust... it's really not going to help much.

So if you have a stock car and just add a CAI don't expect much. They help more when you have a perfomance header and a decent catback. They are better then, but still not as good as when you have the internals built up and some good engine work done. THEN you might see a CAI adding 10-15hp vs the stock intake.