Okay, it's been awhile since anyone has posted here so let me go at it...
I've had my 04' GT for 2 weeks now and I just can't stand the fact it's stock. I originally planned to go 500 miles before modding it but that flew right out the window.
The simplest thing to do is to remove the air silencer and put a
K&N filter in that ugly black p.o.s cone housing. While in the process of doing so, it took me a whole 10 seconds to figure out how to make a homemade K&N air filter kit that deletes the plastic cone housing and breath 10x better than just replacing the filter. Check this out fellas...
What you wanna do is to unbolt the air filter housing and pull it up and let it sit on the side of your engine so to speak. Next, unclip the actual air filter housing and remove the whole plastic cone along with the silencer. Take the silencer and throw it in the garbage. Now if you notice, after removing the silencer there is only about a 20% open hole in the plastic cone that houses the filter so air is EXTREMELY limited going in. The filter itself rests so tightly in the cone that it's almost impossible for any EXTRA AIR to go through. It's forced to suck in through that small opening. So no matter what kind of filter you buy, it does hardly any good by just removing the silencer. So what do we do about this? Easy. Take the snap panel off the plastic filter housing and throw the housing in the garbage so the silencer will have a buddy to play with. Now you should be left with 2 things... an air filter (whether it be a K&N or stock or whatever) and the round snap piece that held the filter housing in it's place. Now get under the hood and you will notice that there's a PERFECT fit to squeeze your filter onto the rubber piece where the actual housing went. But before you put it on there, place the round snap piece around the rim of the air filter (the very edge of it). When you get it tight and snug where it needs to be, snap it in place and you should have a semi-snug fit.
Almost finished...
Even after doing all this you'll still notice some slack. What I did was I took 2 springties about 3" long with hooks and hooked the air filter to parts on the MAF or just anywhere I can find that I can get a tighter fit. Using 2 springties should do the trick. Trust me, this air filter ain't going nowhere! Now we basically have a $100+ dollar high-flow kit that looks bada$$ under the hood. and what did we pay? Nothing.
I'm sure alot of you already did this or either have something similar (maybe even better) and I know there are aftermarket kits that MIGHT flow better but this is for someone who wants cheap and definate performance and can be happy to say it didn't cost a thing. Total installation time = 5-15 min.