from an original article by Scott Martin.
Working as an Air Induction Designer for 6 years for a few of the worlds automotive companies, (VW, Aston Martin, Jaguar, Ford, Saab, Opel etc.) has given me a good insight into what does and doesn’t make a good induction system. There are various types of filter medium on the market with various bold performance claims.
Foam type filters allow a lot of dirt to enter the engine, especially if they aren’t changed regularly. As they use open cell foam the dirt particles rattle around in the foam structure, as the air does, and eventually finds a way through.
Mesh type filters boast the filter down to 20 microns. I have extensive engine wear data showing that particles down to 3-8 microns actually wear big ends and the rings. Being only a thin filter medium there is nowhere to trap the dirt and it only takes a little effort to suck it through. It may be good for flow, although I seriously doubt this, but you want this power and the engine to last.
Cotton type filters (oil treated) do offer better filtration by virtue of the oil sticking and trapping the dirt particles. Our suppliers of air filters have done a lot of work on oil migration to the airflow sensor and have found little proof of this. 1 know people will claim that the oil affected theirs, but as long as the filter isn’t soaked in oil, there is little evidence. We only treat ours with only 10-20 grams of oil. So be warned when cleaning yours. The use of oil on a filter not only improves its efficiency but can also triple the amount of dust it can hold. This is why we only use oil when the vehicle only has room for a small filter and/or works in a dusty environment, (e.g. S/America, Africa etc.).
Synthetic type cone filter has a combination of all the others virtues with NONE if the down sides as I see it. Apex’i is the only company I am currently aware of that make these in a cone type. It has the bell mouth and other air flow aids, and the filter medium they use is recognised in our business as the best. It has good flow characteristics as well as exceptional filtration capacity down to the real fine stuff. The only down side for myself as a designer is the fact it 3 times the price of paper, and making 1 million air box’s a year we tend to look at price first. But for us as an after market item the expensive price of the filter isn’t as important and there are only pennies in it. In my opinion these are the BEST filter on the market.
All/most air induction kit should offer lower restriction as long as it is clean and in good order. But there is the problem of under hood heat. As long as there is some baffling and cool air ducted in this shouldn’t be an issue. The worst condition is actually when stationary, but this isn’t a problem as no power demand is being made on the engine. As soon as you do move off then cool air will purge the system quite quickly.
With regard to the foam filters, yes they do let a lot more dirt in, especially when compared to the factory fitted paper filter, and yes this will lead to premature wear. But when this will raise its head as a mechanical problem, no one can tell.
All I’d say is that it won’t do say 130,000 miles before a rebuild, it may only do 80k now. I don’t know. Is this a problem? You probably won’t own it then, so don’t worry. Its only if your car is a long-term thing, you intend on keeping it forever it may be worth using something else. But it won’t die tomorrow.
As for oil additives, you can buy spray on oil to serves filters for K&N etc. But I would NOT recommend putting it on some foam filters. Oil can do some horrible things to foam. Besides the whole idea is for some foam is to be dry. An oiled one may just completely clog up into an oily sludgy mess. Foam filters use their thickness to contain the dirt, where as paper/fabric and mesh hold it on the surface, and the oil helps this. Apex’i filters do a combination of the two but are dry.
My experience, (motor industry), we cannot afford in the field failures, it buggers up the small profit margin you see. We need every car to do 100,000+ miles regardless in all conditions and environments, hot, cold, wet, and dry around the world. So our standards are very tight.
Quality is also an issue. If you take a close look at a K&N filter, (which is one of the better ones), you will see measurable gaps in the fabric. And when I say measurable, I mean with a good ruler.
As a comparison I have some test data:
This test was done on a Ford Focus air box with after market panel filters fitted. The Japanese brands don’t make any for this vehicle, but it shows the typical characteristics for the filter type. I would expect Blitz mesh to be as pipercross but with the lower dust capacity due to no oil and very thin media.
Notice the face velocity, High velocities can suck dirt off of the element. Also note the difference in restriction. Not much in it considering the down sides.
Hopefully now you can all see where I am coming from.
Well I hope this has helped in some way clear up some of the misleading quotes and claims these manufactures put out.
Just one last thought: at 7500 rpm and standard boost the air filters in an R32 GT-R have to clean 232 litres of air a second and 325 litres at 1 bar, No mean task!