I'm not saying you're wrong, it's entirely possible that a K&N is slightly less efficient than the stock filter. But a seat-of-the-pants reaction and a dyno registering a difference of only 4hp simply aren't reliable for a modification this small, anymore than they're reliable for the people who put the K&N in and claimed they immediately felt more pull from the car. This is a tiny little mod. You would need to be an extraordinarily sensitive person to discern a difference of less than 5hp. That's around 1.5% of the car's power. That's like going to the gym, doing a few repetitions on weights labelled "200 pounds," and saying, "hey, these are 202 pound weights!"

What most people notice is the louder intake noise with the K&N, and that's where most "feel" the power. But even if your K&N did *exactly* what the dyno said, you shouldn't be able to feel a loss of 4 horsepower. It's a filter. You'd have to coat half the thing in cement to feel a difference. Turning on the a/c has a much bigger effect. Turning on the headlights probably has nearly as big an effect. If anything, I'd look at the effect disconnecting the battery has. THAT you can instantly feel.

-Jack
Obsidian '03 G35 Sports Coupe
Titanium '03 MX-5 Shinsen #532

 

I hear what u are saying JDman,
its only a $50 filter i dont expect much from it but what i didn't expect at all was any performance loss however minute it may be (even if its due to other factors). I'm just posting to let people know that for me and possibly others that getting the K&N could be a waste of money for performance gains. Sure the K&N is reusable and over the years will probably save u some money as is has on my previous cars.

03 G35 coupe SS (GD) 6spd everything but navi
02 QX4 pearl white
00 528 Silver on black