K&N Air Filters--Any Cons?

[hoss4659]

Are there any reasons not to install a cone style K&N air filter on a 3.2 engine? I would expect some increase in induction noise, and that is OK. Since the Motronic uses an O2 sensor, I assume it will compensate for the reduced restriction to the air supply and with the closed loop operation there will be no problems with excessive lean-ness of the fuel air mixture. If I am wrong, please point out where and why. Thanks.

[Dpmulvan]

K&n great filters

[mikesride]

Dirt in your engine a concern?????

[Ronnie's.930]

Originally Posted by Dpmulvan

K&n great filters

Agreed - I've used them for over 20 years, on everything from racebikes to a 7.3L diesel (and Porsches, too), and never had a problem of any kind. Some people report an increase in dirt, and/or the oil used on them getting spread around in the intake, but I haven't experienced that . . .

[john walker's workshop]

Hold one up to a light and observe all the holes where fine dirt gets through. Paper for my engines.

[GeorgeM]

+1 for the stock filter.

[McLovin]

Originally Posted by hoss4659

Are there any reasons not to install a cone style K&N air filter on a 3.2 engine? I would expect some increase in induction noise, and that is OK. Since the Motronic uses an O2 sensor, I assume it will compensate for the reduced restriction to the air supply and with the closed loop operation there will be no problems with excessive lean-ness of the fuel air mixture. If I am wrong, please point out where and why. Thanks.

What makes you believe that Porsche wasn't smart enough to design an air filter big enough to supply the engine with more air than it can use?

That's a pretty simple task for even a mediocre engineer, and at Porsche I think they were above average.

[McLovin]

In other words, their are a lot of restrictions to the intake air supply. The throttle body, runners, heads, intake valves, etc.

What makes you believe that the stock air filter is the bottleneck?

[porsche moose]

Dirt in your engine, no HP gain

[tcar]

Dirt.

plus if you clean and over-oil it (almost always happens) you get oil mist screwing up the downstream sensors.

[Reiver]

Originally Posted by john walker's workshop

Hold one up to a light and observe all the holes where fine dirt gets through. Paper for my engines.

Given that Arizona is dusty, fine dust in the heat. I ran a K&N in my carbed hot rod and always found dirt in the throats that would mess up my idle jet.....I always maintained/washed/oiled it properly.
Went back to a paper element and no dirt whatsoever in the carbs.
Ok for a racetrack, not good for the street.

[Steve@Rennsport]

Originally Posted by john walker's workshop

Hold one up to a light and observe all the holes where fine dirt gets through. Paper for my engines.

AMEN to that.

Racing engines are OK with K&N, BMC, and any matter of oiled foam air cleaners since these are rebuilt on a regular basis.

Street engines, OTOH, are expected to last 100K to 200K miles and using anything but a factory paper air cleaner element is totally counterproductive toward that objective.

[hbueno]

I went back to paper filters after seeing how much dirt passed through the K&N and settled in the airbox and beyond.

Hugo

[Oh Haha]

I bought my K&N filter because I have run them on my good weather cars for many years. It was one of the first things I bought for it.


The guys here posting that they use paper are some of the most respected names(to me anyway) and have more experience than I.

However, I have not found dirt in my airbox as others have. I do not drive on dirt roads and MI is not exactly known as a dusty state.

My car has close to 200,000 miles and is still going strong.

[spuggy]

I've been pretty happy with K&N's over the last 4 decades. I don't fit them for HP.

The two most common mistakes seem to be over oiling and cleaning too often.

There's a specific amount of oil you're supposed to use, based on filter area. The recharger kits contain lots of oil. You're not supposed to use it all....

The service interval is 50,000 miles for most people:

The service interval can be from 100 miles in a desert-racing environment to 50,000 miles for normal street use.

It's the DIRT it collects sticking to the oiled element that stops the crap getting through; you don't clean or re-oil a K&N just because it's not that pretty pink color:.

The dirt particles collected on the surface of a K&N element have little effect on air flow during much of its service life because there are no small holes to clog. Particles are stopped by layers of crisscrossed cotton fibers and held in suspension by the oil. As the filter begins to collect debris, an additional form of filter action begins to take place because air must first pass through the dirt particles trapped on the surface. That means a K&N air filter continues to exhibit high air flow throughout the life of the filter while it is accumulating dirt. At the same time, the air flow for an average paper air filter can decrease dramatically as the paper element gets dirty. So as dirt accumulates, the performance advantages of a K&N air filter can increase! Tests performed by an independent laboratory commonly known as the Frazier Permeability Test have shown that the Medium used in K&N air filters flows more than 300% more air than paper air filter medium when compared on a square inch per square inch basis. A Square inch comparison is not directly proportional to the increase you can expect from installing a K&N air filter in replacement of a paper air filter due to the effect of such things as filter size, number and depth of pleats. However, you can be assured a K&N air filter will provide dramatically more air flow which can enhance engine performance.

Both quotes from K&N Air Filter Facts You Should Know

[wwest]

Except at WOT and "full throat" the throttle plate is THE major airflow restriction.

If you're a participant in the 24 hours of Daytona, fine, otherwise....

[gliding_serpent]

Downsides...

1. Cost
2. Fitment (many gte their mesh damaged by the plenum mounting node for the original air box
3. Weight. Weigh more than the OEM intake.
4. Maintenance (more of it)
5. Finickey (see above. Over oiling)
6. Dirt (trust me, not worth the small gain it might give in power, when you consider engine life and costs)
7. Lack of power gains over a open or drilled airbox with a clean filter (Steve Wong told me he runs a open airbox with paper filter and it is about as good for flow as a K+N cone filter, but lighter)

[Jay Laifman]

Here is my completely open, honest answer: the K&N can be great - and I've run them. But, I know me. I'm FAR more likely to simply click and order a new filter from PP and install it, than getting around to the mess and bother of cleaning the K&Ns and then oiling them. Nothing against the K&N. Just my SOP.

[HorstP]

I use a BMC conical filter. It does not provide some of the disadvantage listed by gliding_serpent:
- fits without any issues
- is lighter than the stock airbox
- provides a noticeable power difference to the drilled stock airbox it replaced

It needs a properly designed adapter to create a smooth airflow from the round filter to the rectangular AFM intake. A simple adapter does kill all the gains.
At certain throttle settings it produces quite noticeable noise, but my car is gutted of all interior sound deadening, so it might be worse compared to others

The gentleman who designed the adapter actually suggests turning the AFM 180° to achieve the same set-up as on a 964 engine. I have no tried that yet.

[HorstP]

and this is how a properly designed adapter could look like: