I've got a k&n panel filter installed now and am interested in a cai, are there any differences power wise? And how do they affect sound and overall performance of the vehicle

I know on the EF-AU, a low-restriction filter (panel or pod) usually won't give you a gain you can feel - though it is still a good thing to do. But the BA DOHC engine sucks quite a bit more air, so it would make more of a difference.

The SS Inductions Big Mouth on my EF and AU feels like it made a slight improvement to performance, but I don't know how much of that is just in my head. It does increase induction noise noticeably (especially if there is no sound-deadening under the bonnet), which can be quite pleasant at full throttle.

An NA 4 litre is a 4 litre, whether it be SOHC or DOHC. Displacemnet is the same, will suck the same air at the same revs.



There is little flow difference between the K&N type filter and the factory paper type filter. Advantage of the reusable type (K&N) filter is a cost saving over the life of the filter, add in washing and reoiling it etc and that can become questionable.

CAI increases the cold air intake to the filter system, this is done by either larger intake snorkle or additional intakes to the Airbox from outside the engine bay (heat). F6 intake/airbox has an additonal snorkle that fits up behind the headlight.

That would be true, all other things being equal. But the 4 valves per cylinder gives better volumetric efficiency than two valves - more air mass in the cylinder ('cylinder fill' or 'load') at a given RPM. This is especially true at higher RPM, where the SOHC starts running out of puff. Also, the DOHC revs about 500 RPM higher than the SOHC, so pumps more air again. So, a filter that presents negligible restriction on an SOHC might be leaving a measurable amount of power on the table in a DOHC - especially at high revs.