I put in a K&N air filter a couple of weeks ago and i have really noticed a big change in the car, but a lot of people on this site say that you actually lose horsepower with the K&N. Is this true and should I switch back to my stock air filter?

 

Leave the K&N in there, its better than the crappy paper one...

 

If anything, the KN is more open while allowing more airflow, KN knows what they are doing.

 

Leave it in there, but don't expect no more than 1-2 RWHP difference.

 

Dynos don't lie, or do they? K&N COSTS ME HP. Runs were roughly one month apart in almost identical conditions. Temp was actually 1-2 degrees warmer with the paper filter on 03/08/2003.

 

I don't know about the K&N but the NISMO filter gave me three horsepower on the dyno consistenly. If the K&N flows 50% more than stock I would assume it should give you more power than the NISMO since it is only 30% more than stock.

 

I have also seen dyno's w/ 2-3hp gains when I was searching the mod section a couple months ago, do a search, you should find them.