Intakes are a finicky thing. Some cars gain, some don't. With a good short ram, you can make an extra 5 hp, but with a poor design and filter, you can lose the same amount, as well as introduce your engine's internals to the concept of dust scouring, as almost all aftermarket filters are significantly worse at filtering than stock (I say "almost all" because it's possible that someone, somewhere, has invented an aftermarket cone that filters better than stock paper... but so far, I haven't seen one).
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Hell, some modern cars have such efficient intake tracts and intake tuning that it's near impossible to see meaningful gains with a cone filter and tube.
Turbo cars are hard to pin down. Modern ECUs often pull power if they see something different in the intake tract. A lot of turbocharged cars (WRX, Mazdaspeed3 (way to go designing that cold air intake, Mazda), most CRDis) don't respond well to aftermarket cone-filters, though they do make a little more power with K&N drop-ins.
The only way to know if your filter actually works is a before and after dyno done within the same hour on the same dyno, with the car properly warmed up for both sets of runs. And even then, if your car has a learning ECU, it may just negate any gains in power over the next few hundred miles as the computer relearns its fuel maps around the extra air.
The only simple mod that consistently makes more power is headers. If it's going to be your only bolt-on, that's the way to go.
Not to say that intakes are useless... but you'll only see the most benefit from breathing mods if you have a means of retuning your computer to take advantage of your bolt-ons. I'm making over 35 hp more than stock with simple bolt-ons (intake, exhaust, cams)... with about 10 peak hp of that and 15 hp midrange due to retuning.
