We know we have to replace our engine air filter because if it gets too clogged, it will restrict air flow and reduce performance/economy. But surely, even a clean air filter obstructs air flow somewhat, so might we get better performance and economy if we removed it altogether? Would that upside be significant, and would the downsides be serious? Wesley
Air filters do restrict the intake of air, but over a large surface area so they allow more than enough to get through to maintain the essential 15:1 ratio with the fuel supply regulated by the throttle (accelerator). Although your filter fits in a modest container, if fully spread out, the fibre mesh would be the size of a bed blanket.
In normal motoring, removing a clean air filter would make no difference to performance or economy (or such a small difference you would need high-tech laboratory equipment to measure it).
What you would get more of is noise (an attractive prospect for some motorists) because the “spongey” air filter also does sound-proofing duty.
And your engine would wear out faster, because it would be ingesting the solid particulates (aka dust/dirt) kicked up from the road surface and other sources.
Our air is loaded with that detritus, even when you can’t see it. Some of it is soft or cloggy; other elements (e.g. silica) are hard and very abrasive, however small they are.
Park in a car port for a week and you’ll see what I mean. It will gather so much dust it’s hard to tell what colour the paint is!
The limit on air supply is not the filter – it is the size of the throttle chamber’s throat. That’s what motorsport modifies, to get more air and therefore allow more fuel at the correct mixture to produce noticeably more power. The word economy does not appear in the racing dictionary.
Cleaning an air filter
Air filters are made of a dense but porous mesh of fibres, arranged in mass of deep and closely spaced folded pleats to maximise their surface area.
That presents a barrier to (catches) extremely small particles while also allowing high volumes of air to pass through under suction. Put your hand (briefly) over the end of the air filter’s suction tube when the engine is running, to appreciate how determined that suction is.
Over time and distance, the captured particles start to clog the microscopic air channels between the micro fibres so the air flow is increasingly obstructed – eventually to a point where “not enough” air gets through to achieve the optimal air: fuel ratio.
Both performance and economy are compromised. And as the engine gasps for more air, it can start to pull particles through the mesh, damaging the fibres and allowing abrasive material into the engine, fouling the engine oil and thence abrasively scrubbing all the moving surfaces it is supposed to protect.
Well before that stage the air filter should be replaced. In the interim, the effective life of the filter can be extended, and some cost might be saved by cleaning the filter (once or twice in its lifetime, probably during oil change services).
But if this is done at all, it must be done properly – in a way that removes much of the trapped dirt without (!) damaging or diminishing the integrity of the mesh of filter fibres.
For most “paper filter” types, that means no liquids. It means gentle tapping. And it means no close-range or direct high-pressure air (that will “tear” microfibres).
High-pressure air should never be aimed directly at the pleats. Place the filter on a clean surface and aim the airstream through the centre of the filter at the surface it is standing on.
A strong enough but non-damaging airstream will defect sideways through the mesh, from inside to out – you want particles to go away, not bury them deeper into the fabric.
