Cold air has more oxygen by volume. So you can stuff more fuel into the cylinder while maintaining the proper air/fuel ratio. Thats one reason why the go fast people like it. The idea behind using warm air for efficiency is to intentionally "depower" the motor. Less oxygen by volume means you must open the throttle further to generate a given amount of power. A wider throttle opening means reduced pumping losses.

Btw, the O2 sensor will always strive to maintain the proper air/fuel ratio, so its not running lean. In a way, its similar to driving at high elevations (less O2 in the air), which can be more efficient for a number of reasons.

In practice though, whether it works seems to depend on the specific vehicle and how it's programmed to respond (or not) to the increased air temps. Some ECU's may back off timing to prevent knock, so you end up with a zero gain.

 

Power to weight ratio, I have never owned a peppier vehicle than my 01 2wd Cherokee. When I step on the gas it is gone, more hp will just get me in trouble.

 

Torque

 

Yup. You drive torque and race horsepower. This is because HP is developed at the high end of the RPM range and nobody ever gets up there. At least I don't with my 200k motor.

Torque rules.

 

Horsepower sells cars, torque wins races.

 

Well, it gets me from 0-60 in the blink of an eye, never had it over 70. Pretty much jives with what you are saying. If I ever get my XJ to 140 or 150 and live I should probably have a K&N but I am not sold on the whole cold air thing, not for a stock engine in an XJ.

 

If you get it to 120 youd be running no filter on a drag strip lol and not near a stock 4.0

 

i run a spectra that is the same as a K&N and half the price only been through two tanks of gas so far and seems to have little better responce,havent noticed any mpg yet but it been all in town driveing

 

Somehow I think...say, Jimmie Johnson or Matt Kenseth might have a different idea about clean, cool air when they "check out" to win a race...and those motors run pretty warm!

As for the thread, great info...seein as how Four Wheeler magazine just ranked a CAI as the #3 favorite upgrade (out of 10) . Glad I read this, because I'm still running stock and now I don't have to worry about buying a CAI. Amazing how something that looks really cool can sell so well....

 

I have had no complaints on my CAI, I have had it for 4 years now (transferred it from two Jeeps now) and noticed atlest a 1-2 MPG gain on the interstate driving back and forth to Colorado and Illinois. A kind of drive that MPG's are noticeable... Also it's a lot better to only have to clean the filter on the CAI than buying a new paper filter each time. Others say hold them up the light and notice the different in density in the filters but just because you see larger gaps in the KN filter doesn't mean more filth is getting into your engine, that is where the oil application comes into play and plays a hugs role and still allows air to get through easier but not the dirt and grim. I say go with the cold air kit and keep the same filter for life (of course maintenance is involved though)!

 

REASTON21 I have had the same problems with bad gas mileage. I have been looking around myself and have noticed neon injectors and a new exhaust may help. You should look into those for cheaper parts