CAI's DO help. Trust me, i drive a 4 banger. I made my CAI (with a heat shield of course) myself and it was the first (of a few) power mods i've done to it. I drive the same 45 miles to and from school 3 times a week, going the same way each time and leaving at the same time every day. Before any of the upgrades my jeep was just on the power line of barely being able to use 5th gear with the size tires i have. The day after building and installing my CAI i could tell the difference easily, mostly because it took the jeep all she got to get up the gynormous hill i had to climb to get to school in 3rd gear, almost being able to use 4th but not on the steepest portions. After the CAI i could then climb the mountain in 4th gear and use 5th gear at speeds other than 70+

I wouldnt say a CAI would give an increase of 25hp, but it definitely added a good 15hp to mine. Thats my personaly experience

 

stock air filter setup.... but swapped the muffler (choose whatever brand you want...) and went from 14mpg freeway to 18-18.5 mpg freeway

93 5.2 V8

 

Google 4.0 liter cold air intake shootoit...mopar's cold air intake wins, AEM second with real independent Dyno studies by a reputable magazine...

 

Google 4.0 liter cold air intake shootout....mopar's cold air intake wins, AEM second with real independent Dyno studies by a reputable magazine...

 

I don't remember where I got these figures, but I was told for every 10* lower the intake air temperature gets, you increase the fuel efficiency 3%. All I can tell you is my experiences with my 67 Camaro SS. I took the stock round air filter housing and cut the snorkel off, soldered a coffee can on it, and ran a 4" plastic dryer hose out to the area under the front bumper. On cold damp nights, the car had a noticeable increase in horsepower and fuel economy at highway speeds and a little more "snap" off a traffic light. The setup was a high output 350 with modified metering rods in the Quadrojet carb, a 4-speed stick trans, and 4.10 axle gears. The gearing gave me 4000 rpm at 70 mph and I still got 16 mpg. I think the increase in power was due to the incoming air being slightly pressurized by speed. I did notice the filter getting moths stuck in it though!

SO, getting back to jeeps, air from in front of the radiator is a lot colder than air from the engine compartment, the stock ducting will pass all the air the engine needs, and the flat panel air filter will stop all the debris necessary to prevent engine wear. You just have to change it when it gets dirty. If all you want is to hear the intake howl, buy the K&N or the AEM.