I recently needed to replace my K&N pod filter as it is (b) very dirty, (b) getting dirty very quickly because it is exposed to the under bonnet area; and (c) illegal where I live.
Ideally I want to refit my original air box but this is difficult as my car has an aftermarket supercharger and the original air box is going to need modifications that I don't have the time for at the moment (nor the skill probably).
I looked at what sealed systems were available that I might be able to fit easily, that would solve my problems.
First I found the K&N Apollo closed air intake system which appears to be a good choice. It includes a hole for mounting an original sensor (includes a plug if not to be used). However, although it can be cleaned it needs to be oiled. I don't particularly like this extra level of maintenance and I know there has been discussion about possible issues with oiled filters. Also, the plastic housing makes it quite bulky and heavy, and subsequently harder to secure.
As a sidenote, the K&N kit is quite expensive (A$400), but there are replicas for sale on eBay for a fraction of the price (A$70). The housings look identical, but I'm not sure about the quality of the filter on the replicas. You can however save yourself a lot of money by buying the replica kit but only using the housing and then buying a genuine replacement K&N filter element only (A$135), which I presume would bolt straight on.
I then found these universal carbon fibre kits which appear to need less maintenance and may be easier to mount due to their smaller size and lighter weight.
They appear to be sold under various brands. For example, the SAAS branded product appears to be identical.
They are usually all black but I have also seen one where the carbon fibre body section is white, and a black body with red or yellow end pieces.
Here's a rundown on what usually comes with these kits:
Air filter
The air filter is housed in a container to seal it from the air inside the engine compartment and insulate it from heat.
The filter housing is available in black or white and it is claimed to be constructed from real carbon fibre.
The filter element itself is noted as being dual layer, and washable and reusable repeatedly. I presume it doesn't need oiling like some filters.
I am not sure about what size engines the filter is suitable for, some sellers say it is suitable for all engines including forced induction, but I did see one seller list that it was suitable for normally aspirated engines.
Dimensions: 190mm (body)/250mm (inc. inlet and outlets) long, 132mm wide
Inlet ID: 70mm
Inlet OD: 76mm
Outlet ID: 70mm
Outlet OD: 76mm
Weight: ~400g
The photos below are of the air filter element removed from the body.
It is approximately 120mm wide at the base, and 60mm wide at the top, and 135mm long.
On the outlet side, the body has a removable end piece that has a rounded edge to smooth airflow, although it doesn't extend to the edges where it meets the air filter body.
Mounting bracket
Most kits include a mounting bracket for the filter.
These kits usually come with a clamp that attaches to the filter air housing. The mounting bracket can be secured to this and attached to a secure point of the car body.
Dimensions: ~180mm long, 22mm wide
Turbine
These kits sometimes come without a turbine, but often they come with a single or double turbine fan.
The effectiveness of these fans is debatable. The sellers claim that they improve fuel burn and subsequently there are improvements in fuel economy and engine performance.
My guess is that the restriction to airflow that these devices create would cause more issues than these devices could offer in benefits.
The double fans are noted as being twice as efficient as the single fans (or twice as restrictive?).
They do not need to be fitted and can be left out if preferred.
They are apparently made from lightweight aluminium for strength and durability.
Overall Size: 64mm (2.5") × 50mm (2")
Pipe
The kit comes with a flexible and adjustable pipe that can be used to route air from outside of the engine bay into the filter housing.
The pipe is made of a thin metal so it is flexible but will remain in any shape it is set to. It's length ranges from 230mm when fully compressed to 1 metre when fully extended. It could be cut to length if required.
Length: 230mm (?) to 1 metre
ID: 76mm
Reducers
Different kits come with different reducers, sometimes two and sometimes three.
It seems to be either two 76 (3") to 63mm (2.5"), or three different size reducers - 76mm (3") to 70mm (2.75"), 63mm (2.5") and 60mm (2 3/8").
Dimensions: ~77mm long
Inlet ID: 76mm
Outlet ID: 63mm
Hose clamps
These kits usually come with two or three hose clamps.
These are ~80 mm clamps that are most likely intended for each end of the filter housing.
Legality
This will depend on where you are. Where I am (NSW, Australia), I believe that an aftermarket filter must be sealed and must be securely attached. With this kit it is possible to meet these requirements, which is one of the reasons I chose to try it.
Another requirement is that original sensors must be retained. If the original air box has a temperature sensor, as mine does, you will need to find a way to mount this to this air filter. I plan on just drilling a hole and securing the sensor somehow.
My impressions
I fitted this kit to my BMW 318is (E36) which has a few modifications including a supercharger. Previously I had a K&N pod filter that is not sealed.
Firstly, this air filter kit smells awful - a very strong plastic or chemical smell. But I guess that doesn't matter as it's going into the engine bay. [Could this be that the filter element is oiled?]
Quality is as expected for a product made in China and as cheap as these kits are (I paid A$70 shipped). It looks a bit cheap and nasty and the air filter element does not look very well made (uneven gap between folds), although I can't see any obvious issues with the filter material itself.
The filter housing is very thin, as to be expected, so mounting my inlet temperature sensor is not going to be so easy. I have no experience with carbon fibre but this material can be scratched off and is very thin, and this exposes the underlying housing material which is plastic. The "carbon fibre" scratches quite easily and mine got plenty of scratches during installation.
The air filter element came with a small piece of loose fabric on the engine side so it is worth ensuring that there are no foreign objects before fitting.
The size of the filter looks to me to be similar to most aftermarket pod type filters (perhaps narrower but longer) so I am not concerned that it might be too small for my supercharged four cylinder engine.
No instructions are included with these kits so I am not sure on how the element can be cleaned. I think am going to follow the instructions on AutoAnything which is basically just to vacuum it. (Update: I found one listing which says, "can be washed for long term use, it is reusable.")
The mounting bracket looks to be suited to mount to narrow hose clamps, but the hose clamps that come with the kit are wider than will fit. It may have to be cut to suit your application. It seems strong enough for the job. I ended up buying another slightly longer bracket and used that instead.
I needed to fit the original air intake temperature sensor that is usually mounted inside the air filter housing. I drilled a hole on the intake side of the housing and then secured the sensor to the housing.
The two hose clamps that came with my kit are the type that are suitable for silicone hoses, which is good news.
The reducers (two of 76mm to 63mm) appear to be made out of rubber.
The kit came with a single turbine. Although it seems of a reasonable quality (cast aluminium blade with bearing), it looks to be a big obstruction to airflow and it does not spin with the ease which I would have expected. I haven't and won't be installing it.
I found the kit easy to install and haven't noticed any negatives since installing. It's actually noticeably quieter than my previous open K&N filter (I can barely hear my supercharger now unfortunately), although still very loud under hard acceleration. If you are switching from an OEM filter then you will probably notice a big increase in noise.
Here's a list of brands and models that I have seen these filters sold under: SAAS, CNSPEED, KRICNG, RYANSTAR RACING, Autloader, PQY RACING PQY-AIT13, RASTP RS3-OFI012, HDI AF-CA01, TANSKY TK-FB2303-NF, EPMAN EP-FB2303-NF, AUTOFAB AF-FB2303-NF, VBESTLIFE, VGEBY, WALFRONT, Hilitand, DOACT, JX-LCLYL, wz heng, BesT RyingL 76655, and Mayitr.
There is also a smaller version available. It is known as model IP-002 and it is 120mm long instead of 190mm. These are usually all black or black main body with yellow end pieces.
Update (November 2018):
Thanks to Rob, who posted a comment below, we now know that these filters appear to be a copy of the BMC Air Filter brand's model CDA - Carbon Dynamic Airbox (I've seen these selling for A$350!).
The CDA uses a cotton filter material that is preoiled. BMC say that these should typically be "regenerated" every 15,000 km. Perhaps the copies also need to be oiled?
The cheap version appears to differ on the outlet side. The BMC bellmouth extends to the filter body, but the cheap version has a trough around it.
Unfortunately BMC doesn't provided any details on what size engines these are suitable for, although they do offer different kits for specific cars including 4 cylinder and 6 cylinder powered models one of them being the E36 M3.
A couple of people have asked which way these should be installed (as there are no instructions). See the attached diagram for the CDA to see which way it should be installed.
Update (January 2019):
Rather than cleaning my filter I just bought a new one. I found them selling for just over A$30 on Aliexpress.com now.
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