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Originally Posted by awdsubs
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It's just a filter, aka CAI, althougth it isn't really cold air as there's no ducting for cool air, it just takes it's air from the engine bay as per normal.
Gains will be due to less resistant filter (also less filtering ability) and larger diameter filter.
The stock airbox is designed to protect the filter, has a drain plug for if it gets wet and reduces dust/mud contact. It is also designed to limited induction noise.
If you off road a high rise snorkel is the best bet. And really should have any affect on performance.
This intake will be at more risk when off roading than a stock setup. I also highly doubt their claim of 15bhp increase.
I would expect crisper throttle response and if dirven sensibly better mpg (slightly) but worse mpg when you get on it. A small increase of 5-8bhp would be IMO nearer the mark.
Personally I don't like k&N filters much - SHOCK SHOCK I know - but I'll explain why. And I also respect that k&N have a MASSIVE market share and many will claim to have used their products with great results, although simply claiming great results without comparison is pointless. Or you'll find someone has a dirty clogged stock setup and replaces it with a k&N setup and attributes all the gain to the filter itself as opposed to just have in a clean filter.
Anyhow, back to the K&N issue. Essentially k&N filters are cotton weave, this means they are layered cotton with an oil coating. The oil is there to enhance filtering ability and prevent water ingression.
A clean k&N WILL out flow an OEM stock paper filter. However it will also filter worse, and at the end of the day the whole point of an air
filter is too filter the air.
Paper filters also last quite well and as dirt builds up and they clog they will still flow at a similar rate to a clean one, it's only when they get very dirty that they suffer.
Cotton weave filters clog up quicker and very easily will end up flowing far worse than a paper one does. This IMO is reason a lone ont to run one.
This then means you must clean a cotton weave filter more frequently than you would need to change a paper one.
Now this is my real gripe with k&N's and all cotton weave filters. The cleaning solution generally cost about the same or more than a new paper filter does. And it doesn't stop there because once you have cleaned the filter you need to re-oil it as well. Which adds another cost into the bargin, combine this with the high purchase cost of the filter in the first place and it means:-
K&N filters:
-expsnsive to buy
-expensive to maintain correctly
-requires more frequent maintanance
-worse filtering
-if dirty worse flow
And it doesn't stop here. While re-oiling isn't particulary difficult it is suprisingly easy to "over oil" the filter, the oil then gets onto the MAF sensor which causes false readings and poor running, i.e. more cost and hassel.
NOTE: If oiled correctly then there should be no issues with the MAF.
What I would do and will be doing on my brothers 3.9 Vogue Range Rover is make my own CAI.
Foam filters generally appear to be superior to cotton weave, as they are used extensivly in off road motorsports, both bikes and 4x4's. However not ALL foam filters are and there are many which filter particulary poorly.
I have already bought the filter, it's a large foam filter by Piper X and it cost £12.50 all I need to do is remove the stock air box and attach it.
Again personally I wouldn't use metal tubing on a intake as it is prone to heat soak. My preferred choice is a length of silicon hose. You can buy it from many places and it isn't expensive, but it is rigid and suitable (is used for coolant systems and turbo piping).
You can also buy silicon hose in straight lengths, 45 and 90 degree elbows and with reducing sizes from one end to the other.
With a little thought and a little reading you should be able to make your own "better" CAI for around $50-100, I'm aiming at about £30-40 in total to do the one for my brothers Range Rover.
