I am looking at the possibly of buying a AFE or KN Cold Air Intake for my 2008 Scion XB. The reason I am thinking about buying one is that it would be about a $250.00 upgrade to add a little more power, Enhance the engine sound, and customize my XB. However I have heard that actual horsepower gaines/ MPG gains are fabricated and CAI‘s actually hurt your engine. Right now I just have a TRD(Toyota Racing Development) high-flow drop in air filter. I havent really noticed any improvements with that. Any car experts that have educated advice on this engine modification is apperciated!
The basic idea of a KN or various other Cold Air Intakes is that by supplying cold air and more of it to the intake, you increase the power output of the engine. More air, either by total volume or by being denser (ie, colder) produced more power only if the lack of air is a bottleneck in the engine. If you allow all the air the engine can use in, and then more, guess how useful that extra air is? If you happen to have a highly modified engine where lack of air is causing a performance bottleneck, then this is something that can give real performance gains, otherwise the reality is that you are likely to see little to no gain, and maybe even a loss (because Cold Air Intake is a bit of a misnomer, and quite often they let in more hot air from the engine compartment). Also of note is the way they work: they flow more air by filtering less. While they claim to do as good of a job, I've not seen an independent tests that backup these claims and it seems likely that at best, they will not filter as well as a denser element. You may also have problems with the reusable elements if they are over oiled. In dyno tests I've observed where there is attention paid to methodology, and on stock or mostly stock engines, such intakes sometimes provides gains in the 1-3 hp range, although sometimes also result in losses of equal amounts or a little more. If you have a new filter in the car already, you will probably not see any gain with such a change (although you will get more induction sound from the engine). If your current filter is old, then you will see a gain, although it is about the same gain as you would see with any new filter.
simple fact - they don't work on injection systems in fact they cause the ecu to run a cold start program which enriches the fuel and wastes gas, if something as cheap and simple as an air filter increased power and gave better gas mileage don't you think the manufacturers would all fit them even as an option, also on lean burn engines the colder denser air would make the mixture even more lean leading to burnt plugs and valves, the ecu/maf/temperature sensor are all mapped together upsetting the balance would cause performance to deteriorate, the injection system squirts a measured amount of gas at each cycle so more or colder air would make no difference, unlike a carburetor which supplies gas continuously
