Working as an Air Induction Designer for 6 years for a few of the worlds automotive companies, (Ford, VW, Aston Martin, Jaguar, Saab, Opel etc.) has given me a good insight into what does
and doesn't make a good induction system. I recently removed my air box and after quite a lot of research I decided to go for an M's system. This is just two aluminium adapter funnels, the same as Blitz, with K&N's.
My logic behind this decision is as follows:
HKS type foam filters allow a lot of dirt to enter the engine, especially if they aren't changed
regularly. As they use an open cell foam the dirt particles rattle around in the foam structure,
as the air does, and eventually finds a way through.
Blitz Mesh 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 no where to trap the dirt and it only takes a little effort to such it through. It may
be good for flow, although I seriously doubt this, but you want this power and the engine to last.
K&N type oil treated cotton filters 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 air flow sensor and have found little proof of this. I know people will claim that theirs
was effected by the oil, 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 can not only improve 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.).
Apexi's cone filter has a combination of all the others virtues with NONE if the down sides.
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
is only pennies in it. In my opinion they are the BEST filter on the market.
So why did I chooses the M's system. Well not wanting to sound like a tart, but the M's system
looked a lot neater and factory fitted look when compared to the Apex'i, and the performance
isn't that far behind the either. So for me K&N offered adequate protection as well as aesthetics.
All/most aid 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 the 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.
Well I hope this has help in some way clear up some of the misleading quotes and claims
these manufactures put out.
Just one last nugget of information: at 7500 rpm and standard boost the air filters
have to clean 232 litres of air a second and 325 litres at 1 bar, No mean task.
For more infomation and to see what I mean go to: www.mkiv.com/techarticles/filters_test/1/index.html