K & N Air Filters - Daz
Heard a lot about these. Are they actually any good? do they really increase power? They seem very expensive any idea how long they last?
K & N Air Filters - Dizzy {P}
I think these are the filters that I tried on my Triumph 2500 about 17 years ago when I changed from fuel injection to twin carbs. I found the noise level to be too high (normal air filters help silence the air intake) and they seemed to upset the air/fuel mixture ratio so I got rid of them. That's the total of my experience but I'm sure others will know more.
K & N Air Filters - madf
I had one on an old Mini: definitely improved responsiveness at cost of more noise.. and can be cleaned without replacing them so cheaper in long run.

But modern acrs are tuned for best performance so modern air filter assemblies are MUCH better designed.. On latest Ford Fiestas where I looked at changing, extra power was negligible nad extra noise was noticeable.

Personally I would not bother.. unless as a cheaper long term maintenance cost saver (no new filters to buy)..

K & N Air Filters - Cyd
K+N air filters are very good indeed. What is highly unlikely is whether one will make any difference to your car.

In standard road car, the biggest restriction to air flow is not generally just the air filter. There's the valves, inlet tract, throttle body etc etc. Simply changing the air filter may give you a few more mousepower, but the biggest noticeable difference will be noise (if you're using a direct intake type). Even if airflow is improved, your engine may not be able to make use of it depending on the design of the fueling and ignition systems.

On the other hand if you have a finely tuned rally or race engine then you would definately need something like a K+N to get the best from it. In this instance the wrong choice of filter could have a disatrous effect on engine performance.

K+N do a range of 'replacement' elements where you replace the paper filter with a K+N but leave the air box alone. Again this may give you a few more mousepower, but the biggest benefit will be that you'll never buy another replacement so over about 4 years or so it will work out cheaper.
K & N Air Filters - Ben {P}
I do not think much of K&N filters, especially on standard engines.

K&N filters have been proven in scientific tests to be worse at filtering than standard mann paper filters. In the test i read the only filter to offer a flow and filtratin advantage was ITG, but these are very expensive. I have used these types of filters and noticed far more dirt getting past the filter and into the metering head, which lead to marginally reduced performance.

9 times out of 10 i think the money could be better spent elsewhere on the car.
K & N Air Filters - SjB {P}
Paper filters are fine when new, but clog relatively quickly.

Between 1984 and 1992 when I sold it, I used THE SAME K&N filter on my tuned MG Metro (quite extensive mods), and NEVER CLEANED IT.

With 90,000 odd miles under the wheels, a piston ring broke, and I had to rebuild the engine and gearbox (in sump) from the damage caused.

The cylinder bores were still beautifully honed, with negligible ovality. This would not have been the case if the filter was letting in all manner of particles.

The K&N filter was still spotlessly clean on the inside face, fuel consumption never wavered throughout, and so engine breathing remained the same, too.

The one downside was indeed noise, but the straight through exhaust was sufficiently, err, 'melodious', that a bit of filter noise was neither here nor there.
K & N Air Filters - Ben {P}
If you had never cleaned the filter, it may well then have filtered the air reasonably, but you would have removed any reason for fitting one in the first place (other than noise). The flow through the filter after all this time must of been terrible.

If you factor in the cost of one of these filter systems, then the cost of a cleaning kit etc, you could buy many many paper filters in its place.

Modern cars have filters much larger than those required for the power output of the engines. This is so that if people neglect to change them, or they drive in very dirty conditions, the car still runs fine. I tested one of my past cars on a rolling road with a k&n panel filter, a paper filter, and a paper filter that was half covered over. There was no measurable difference in power produced. Fitting an item such as a performance camshaft is far more likely to produce enjoyable performance improvements.
K & N Air Filters - SjB {P}
The primary reason I fitted a K&N filter was improved filtration quality (rather than additional breathing), with a secondary benefit being reduced cost. I had no intention of extra power from the filter. That came from a zillion other modifications that cost rather more.

The filter cost only twenty quid, and fitted in the standard case (no expensive kit), but because it had so much more surface area than the Unipart paper one, would still flow enough air for my heavily modified engine to breathe properly. It would also keep flowing enough air, and filtering it properly, without clogging up over time.

That the engine wear was negligible after 90,000 miles vindicated my primary reason for going down the K&N route, and the fact that it was CHEAPER (one off twenty quid, and no cleaning kit is cheaper than 90,000/12,000 x £10 each ) was a minor additional benefit. Horsepower, as I said, came from other mods, not the filter.
K & N Air Filters - Ben {P}
If i could find the web-page i would post the link here that shows under decent lab tests that filtration from the K&N filter was significantly worse than the standard Mann paper filter in the test. ITG filters on the other hand were significantly better.

I accept your point regarding reduced costs. I am used to common cars where i can get air-filters for a few quid.

If the air filter was fitted in the standard case, and was therefore the same size and shape as the original, how did it have much more surface area. Further to that if the filter filtered properly why did it not get covered in dirt- where else could all the muck possibly go?? You could even use the same argument to suggest leaving a paper filter in for 90k miles. No manufacturers suggest this however.

How can you possibly conclude negligible wear was due to a filter, surely other factors would be rather more important. Did you run an engine for 90k on a different filter in the same conditins as a control.

As i have said i will post the data if i can find them showing flow and filtration properties of commonly available air-filters.

It look slike we will have to agree to differ untill i find the evidence.

What had you done to your engine?
K & N Air Filters - SjB {P}
I have seen the data you refer to as well, Ben, but as always, I speak as I find. In my case, a K&N filter worked. Perfectly, in a real life test more representative, especially in duration, than any accelerated bench test.

The K&N filter I fitted had more surface area by having more zigs and zags in the same diameter than the Unipart paper filter. The standard (donought with a hole in the middle where the SU carb sat) housing had a more than large enough volume between the outside of the filter and the case, so the result was that until really clogged (which didn't happen in eight years), the engine would still always breathe enough air as the filter got dirty.

How can you possibly conclude negligible wear was due to a filter, surely other factors would be rather more important . I didn't say that. If the K&N wasn't any good at stopping muck getting through, I would have had a worn out engine in no time, let alone after 90,000 miles. Try running an engine with no filter at all, and see how long before the bores are clapped out. My MG's bores still had excellent honing marks
from when the engine was new, and it consequently didn't burn any of its' expensive Mobil 1, either.

So, to conclude, in my experience the K&N filter is at least no worse than a paper filter at filtering, and is a lot better at resisting clogging.

Mods to the engine?
Buy David Vizard's 'Tuning BL's A-Series Engine', and look at what you typically need to have a tractable, torquey, 1380cc A-Series putting out 90 odd horsepower, and you'll have a good idea. Standard was 1272CC and 72 horsepower, and the additional grunt belied eighteen horsepower. Still miss the old rust bucket, the latter comment being why I eventually Got Shot.
K & N Air Filters - Ben {P}
I was lucky enough to find that book at a local library- excellent. The development work he does on that head is amazing, four chapters worth if i remember rightly!

I still think ITG filters are better though. Dont know what it was with mine, i kept getting crap in the metering head with the K&N panel filter. I don't doubt it filtered once it was filthy, but i cant see how it could allow much air through with 90k of dirt on it.

I understand what you mean now regarding the surface area of the filter. Why did you choose to stick with the standard filter housing, considering all the other work you did on the engine?
K & N Air Filters - SjB {P}
Why did you choose to stick with the standard filter housing, considering all the other work you did on the engine?

Simply that the MG Metro manifold is one of the best you can get for an A-Series engine, even spending a fortune from one of the specialist tuners. It flows well, especially with some minor port work to stop reverse flow on over-run, and vapourises fuel well. The SU carburettor, with a few tweaks such as modified venturi, needle, damper assembly, and butterfly, was also ideal for the torquey street motor I wanted, and amazingly, so proved to be the standard MG Metro filter housing. In other words, everything worked in harmony.

Prompted by this discussion, I have just had a very enjoyable trip down memory lane for a few hours, dusting off the book I mentioned, which I hadn't previously touched in (many!) years. In the section "Standard Filter Cases - Just How Good?" I found "The MG Metro for instance has a system which is more than adequate for the standard power output of the engine. In fact it's good for up to 85 and may be even 90hp, and on an engine such as this, because the case design is essentially good, it is easy to make a small but worthwhile gain installing a K&N replacement element in the standard case."

Well, this is what we did indeed. In the event, even with a tuned motor that needed more air, the K&N gave me hardly any power benefit over a new paper filter, but it did give the other benefits mentioned throughout the thread, and I was delighted with it. Out of interest, we found that torque characteristics were improved if we kept the standard (long) induction hose connected to the airbox too, but the one area of induction where we deviated from standard was to stop hot air ingestion by sealing the flap in the base of the filter housing closed. Hot air is great in moderation for ultimate fuel economy, but not for horsepower. Cold running was hardly affected, especially as the A-Series is not a cross-flow engine, so exhaust heat quickly rises to warm induction components.

All these years later, I'm now a boring 39 year old with a Volvo V70 2.4T. A fantastic car, without doubt. Quick. Quiet. Efficient. Well made. Loaded with toys. Acres of space. All characteristics way beyond what an MG Metro could even dream of. It might even not crumple like a paper bag (thankfully I never found out in the Metro, and don't want to in the Volvo) Despite all this, that car had an amazing charm in equal quantity to that wonderful offbeat exhaust note from stainless tuned system and the engine's siamesed ports, and I still miss it. I also spent time and money making it handle and stop even better than the motorised rollerskate that left Longbridge, but that's another story!

Time for bed now.
Good night!
K & N Air Filters - Andrew Moorey (Tune-Up)
There seems to be a growing problem that oil soaked cotton filters like the ones mentioned are damaging the delicate sensing surfaces on modern fuel injection air mass sensors.

Simplicate and add lightness!!
K & N Air Filters - DysonC
Like any add-on, it is a compromise. It does allow better air flow, but slightly less filtration and greater induction noise. To gain any performance increase, you must adjust the mixture accordingly (needs to be slightly richer due to the increased in air entering the engine).

Ask Honest John

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