K&N Air Filters

I would want to say not yet. The '04's hav not been around long enough.

However, I'd recommend not buying one and save your money, unless you are only buying it for the reusability factor. Their claims of performance improvements are suspect at best.

 

I kept exact record of gas mileage for one year prior to installing a K&N filter on my Mazda PU and have kept records for the years since. No observable difference in mileage. Cleaning and re-oiling the filter is not really worth the dollars saved on replacement.

I think that maybe if you drive with the throttle wide open most of the time there would be an advantage. I'm thinking of racing or pulling heavy loads. I'm still running the K&N on my Mazda because I spent the money. I won't be buying one for my Prius.

Go to www.bobistheoilguy.com and search the forum on K&N filters for some knowledgeable opinions of the quality of filtration.

John

 

If you are changin a filter with an identical K&N filter, there isn't really much difference. If you have a type of car with a restrictive airbox on it and replace that with an open cone filter, then that can make a difference in both mileage and HP.

 

Forget the claims. A K&N filter will not filter better. It offers less resistance simply because it filters less. For a high performance car that is not intended to be kept running for a long time, there are some advantages. For the Prius, there is nothing to be gained.

Look at K&N (preferably one with some usage) so that you see through the single layer of cloth filtration. Do you see the size of the openings? This only gets worse with time, and the oil spray (no matter how religiously applied) does not help make up the difference of having a uniform, tight filtration surface. Besides, that oil material will get pulled into your intake tract, potentially affecting sensors and flaps; and, providing a general stickiness that can lead to particulate deposition.

If you want, change your stock air filter ahead of schedule. Your car will both "live" longer, and breath easier. And bear in mind, changes to your airbox layout (with or without a filter type change) can be detrimental to your car's pollution control (mostly the passive VOC emissions).

 

Best reported resuts with K&N air filters seem to focus on larger diplacement inline or V-6 or large bore V-8s.

Especially larger trucks, buses, motor homes, etc.

I use one in my Toyota 3.4 litre T-100 with noticeable improvement.

I do not intend to use on in my Prius, however. A very different engine, very differenct application.


Bob

 

Makes you wonder if the engines they emphasize are those that don't have optimally sized air inlets given their displacement size. Automobile designers go to great lengths (under regulation) to muffle the intake trake noise, and to provide cooler air from the front of the car. Given the size of the Prius engine, this was probably not much of a hindrance.