I have a 2003 accord with the 2.4 L engine. I am considering replacing the stock air box with a k&n cold air intake. Just wondering what to expect as far as improved performance, gas mileage and hp. Also, if anyone has done this, would you recommend replacing the pipe andmuffler from the cat back . Maybe a magnaflow or something along those lines.

 

K&N intake will give you a few extra hp and some noise. if I were you I would buy a cheap generic intake off of ebay and slap a K&N filter (or comparable) on the end. Save you some dough.
Cat back exhaust - maybe a few more hp.
Better gas mileage? - I don't think so. It will probably be about the same.

 

 

I've actually often lost gas mileage cuz i can't keep my foot off the pedal... the few times (mostly when i'm dog-*** sick) i've managed to not ride the car rough it got about the same mileage, maybe a tad less but nothing to cry over...

as always, i suggest the Greddy SP2 for the exhaust

 

Dont buy cheap if you can afford quality. You often get what you pay for.

 

Techincally, if you help the car breathe better it increases gas mileage (only very very very slightly)...but most people, like me after installing aftermarket parts, love to hear the engine purr so as a result, mileage slightly suffers.

 

I placed a K&N Cold intake on my 95 accord once. It was the loudest thing I have ever heard. Took it off and sold it to someone else on ebay within a week. I think that is what you will have to deal with with all intake systems. Make sure that is what you really want first.

 

My brother's CT Icebox sounds sweet!!! When VTEC isn't on, it sounds basically stock, but when he hits it, it sounds similar to the Suburban that I just rented for the weekend.

 

But thats a good thing. Let 'er breath! lol

 

This is the dumbest thing I have ever heard when it comes to intake systems. The only expensive peice you need is the cone shaped filter itself. The "intake" is a pipe. A pipe is a pipe whether you pay $10 for one that has no brand name on it or you pay $160 for the exact same pipe that says "K&N" on it.
Just because you can "afford quality" doesn't mean you're getting quality. It just means the manufacturers like K&N think you will be stupid enough to pay $160 for a plastic (or metal) pipe when you could get the exact same thing on eBay for $10.