Induction kits

Ish, you normally use the air filter box as a resonant chamber so what happens before that may be lossy but it doesn't help tune your engine.

Hmmm, don't you ever apply full throttle ? I tend to do so every single time I overtake :)

Absolute tosh. The oil-coated K&N style filters usually give better filtration than their paper counterparts !

Not according to any tests conducted by anyone other than K&N.

Why would car makers fit inefficient air filters? Do Land Rover etc use K&N for their 'safari' vehicles?

Of course. How else do you get the car to change down? ;-)

An equally good question might be why K&N specialise in producing inefficient air filters, if they do so, which doesn't seem too obvious a conclusion.

As far as I am concerned, air filters have two basic properties, they filter out dirt and permit through air. As a first cut, I would expect a filter that was good for airflow, to be bad for filtering, and vice versa. Therefore, removing the air filter altogether is best for power, but dumb because a single grain of sand being sucked into a cylinder means it will scratch up and down the liner until the piston isn't doing anything much for you.

Judging only by the seat of my pants, K&N seem to be slightly less restrictive than most of them, and I'd reckon all filters halt particles of sand and that, so realistically it's a subtle balance between a little more airflow and a little more (non-critical) dirt to go with it, meaning more cleaning is necessary. Must admit, I've not actually measured the pressure gradient over a range of filters directly, which would probably give some sort of objective measurement.

I would imagine there are hugely expensive types of filter used in top competition, but a search didn't turn many up so I dunno how much significance the filter has, might be very small, in which case the point about K&N and foam and whatnot is you can clean them from time to time instead of having to buy a new one, a worthwhile feature even if there is no other difference.

The other observation, which is quite key, is a filter OEM probably isn't suited to a modified engine and you have to come up with some alternative means of getting higher airflow into the engine. Conical filters are a convenient way to achieve this quite easily, so in a sense you have a lot less choice once you move away from a standard engine.

I use my arm, cos my car's a manual :)

They don't. Paper filters are "good enough" - why would the car maker fit hugely more expensive oil-coated foam/cotton elements ?

Nope - why would they ? Paper filters do the job fine, providing they're changed regularly.

Just because a paper filter is "good enough" at filtration, doesn't mean it can't be improved though :)

Care to illustrate such tests ?

All the write-ups I've ever read, have said K&N's oil-coated cotton is very good at filtering. The same doesn't apply to the foam-type filters used by Pipercross and the like though.

AFAIK Aston Martin use them!

Well, they once did. 'Oil bath' filters were the norm at one time. Till technology moved on and more efficient filtering became affordable.

That's the point. A K&N neither improves filtration or flow - unless you compare it with a blocked paper one. And its filtration is considerably poorer than a paper one within its service interval.

There's plenty of independent research to support this. K&N are fitted for looks and or noise - not improved performance. Indeed, they can often

*reduce* performance - a prime example being the Rover V-8 injection as fitted to the SD1 Vitesse, etc.

The message from "Martin \(Please note spammers email address used\)" contains these words:

That's quite likely 'cos they're produced in such small numbers that it's cheaper to buy in a filter than develop one in-house.

Some alternative inlet arrangements , including alternative air cleaners and induction kits , as well as producing increased noise levels and potential icing problems when cold , can produce significant power loss. Cars that use by-pass type MAF sensors (e.g. many Fords , Nissans Jaguars etc.) , reley on the air-flow through them being reasonably laminar to meter correctly , indeed the engine's 'calibration' will take account of this. We have measured , for example on a Mondeo 2 Litre , a drop of 8 BHP in the mid range when a certain well known (and highly hyped up) make of air filter was fitted in place of the paper original. Mike

And they can often reduce power indirectly, because they can encourage poor location. Example is the much-used fitting of two K&N cones to Rover V8s with twin SUs. 99% time they're slid straight onto the intakes of the carbs, which means they'll soak up all the underbonnet and engine heat, and they're certainly not in the line of fire in terms of airflow. It seems very few people consider keeping standard trunking in place, and fitting the K&Ns ahead of this.

Of course not. They're fitted for looks and noise, not improvements in performance.

But it improves both - that's the whole point ! Most top-level motorsport cars use the oil-coated-filter setup - they don't use paper filters. Specifically, a BMC filter-equipped car won LeMans for about the last 5 years running !

But it's not !

Poppycock.

Huh ? You can't see or hear your filter element ! I'm not talking about cones here.

No, you're talking about cone filters. A completely different story.

So they're obviously excellent then. If they weren't more than a match for a paper element, then Aston would be using said paper element !

Are you saying that current Astons use them? Older ones used all sorts of bought in rubbish...