Hello, i want to add a cold air intake to my mazda 3 GX 2013 hatchback but some people told me I can buy only the filter and it’ll work but I’m not sure if it’s true or if I need to buy the whole thing? Also, what is the size in mm I need to buy?

 

There are many CAI available for you Mazda. Just find one that meets your budget. You can also get a drop in filter like a K&N which will work very good. Unless you find someone that has the "EXACT" engine modification that you do and had a base line Dyno followed up by a Dyno run after the performance parts were in stalled and the Dyno operator used the baseline information to duplicate the base line Dyno run there is no one that can with real information tell you if any aftermarket CAI or performance air filter will do any engine power gains!

However Cold Air Intakes sure look "RACE" ! So having them to see when you pop the hood is "KOOL"!
The other attribute that most CAI have is you will hear the intake air more pronounced perhaps supporting the BUTT DYNO increase in power?