cleaner air and more of it!
more power and better fuel efficiency
Hate to break it to you. But a "performance air filter" doesn't generate clearer air, it does the exact opposite. By cleaning air you're creating a bottleneck. Air flow is only as fast as the filter. By running no air filter you'll notice nice spike in power, but exponentially increase engine wear.
It is a matter of risk vs reward. Does the small increase in power (on average you get 1-2% boost with "performance" filters) justify the shortened engine life? If you rock a race car and replace the engine regularly, crack on. But for a daily drive?
What you want to do is create cleaner flowing air, most direct path from intake, intercooler, turbo, inlet, engine. Now you want as much turbulence as possible inside the engine, but before all it'll do is slow it down.
As with "chips" the vast majority just put in a resistor between the MAF and the ECU so the engine believes the air is colder and increases fuel accordingly. Running rich is a lazy tuning method and proves to be very expensive as the excess soot generated will knacker your turbo in no time.
And don't get me started on the inaccuracies in "dyno proven" chips. A dyno is only as accurate as the operator.
1st, never bother with "flywheel compensated", there is no scientific measurement, so it is based on a guess for laughs, stick to power at the wheels.
2nd, never let them run a smooth filter, as the same engine can appear as though it has a 100% increase in power just by running smoothing filters. Back in college I was able to get my 60bhp van to read 100bhp by playing with filters, pre-set in the computer so all that had to be done was tick a checkbox then run the test again, no one would ever know but the operator. Perfect if I wanted to will wave or sell BS products.
They are excellent tuning tools if you use them correctly, that is, record a baseline make your adjustments and then run another test. Rinse and repeat.
Of course, I could be wrong.