Does anybody know what the inlet pipe is like on a 2.4 20v jtd? Is it similar to the GTA or more restrictive? Going to start playing with my car once I've changed the clutch..
As for air filters in general, take the Mighty Car Mods piece with a pinch of salt. It's not as comprehensive a test as it seems. The restriction of an OE setup is mainly the airbox itself and compromised piping, rather than the filter inside. That's going by tests done by a tuning mag in the UK.
In general, cone filters will offer less restriction and more power on Turbo cars. Simply by making the compressor more efficient.
For both cone and panel air filters the least restrictive material is a stainless mesh, then foam, then cotton/'paper'. The same order is true for engine/turbo protection; stainless the riskiest, paper the safest.
In my experience N/A cars are more responsive to the characteristics of the intake piping rather than the filter that's on the end of it. Changing the tubing diameter, length and route is a bit like changing cams, in that there is a sweet spot in the rev range and you move it around. It's not as large an effect as a cam swap obviously. You can move it around but increasing it by a lot is hard work. On an N/A engine a correctly designed (pressurised) airbox will aid cylinder filling, while on a turbo having a huge filter is most important.
It's worth noting there is always a pay-off between air speed and maximum flow, especially on N/A engines. That's evident by the use of multi-route, variable plenum chambers in performance models. You want a long thin straw at low rpm, and a wide short straw at high rpm. A similar story to the primary runners on an exhaust manifold. The same rules apply to turbo engines, they're just not as sensitive because the air is already being forced in at high pressure by the turbo.
Not sure if I've helped or just rambled? This info is a combination of theory and experience, so feel free to take as much or as little on board as you like. Bottom line is air filters aren't just for sound. I'm going to be playing around with my induction setup on a budget. Not sure exactly how yet.