Injen has been building cold air and short ram intake systems in Pomona, California since 1997. They engineer each kit around a specific chassis and engine combo, not a one-size-fits-all tube with a filter slapped on the end. That matters because intake length, diameter, and pickup location all change how your engine pulls through the RPM range.
Their SP series (short ram) tucks under the hood for a quick install. The cold air setups route the intake tube down behind the bumper or fender liner to pull cooler, denser air. Cooler air carries more oxygen per volume. More oxygen means the ECU can add more fuel. You feel that as a sharper throttle response and a wider pull through mid-range RPMs.
Injen uses their SuperNano-Web dry filter media on most kits. Dry filters skip the oiling step that catches people off guard with oiled cotton gauze setups (over-oil a filter and you can foul your MAF sensor). The SuperNano-Web element flows well and cleans up with a rinse instead of a re-oil kit.
Fitment is model-specific. Injen publishes CARB E.O. numbers for a big chunk of their catalog, which means those kits are legal in California and other states that follow CARB emissions standards. That alone sets them apart from a lot of intake brands that leave you guessing at smog time.
You get a solid intake sound bump too. The open filter element and mandrel-bent aluminum tubing give you an audible growl on throttle without droning at cruise. If you want your car to sound like it woke up, an Injen intake is one of the first mods worth doing.
