SeanR

I've got 6 of them sitting here and Rog has about a dozen sitting around. Don't know why I'm holding on to them, suppose I might get lucky and someone with an OB will want one.

Hell, get rid of the entire air box and put on this. Debate solved.

Optimator

Here’s my two cents. The K&N does not filter as well as OEM, but the difference is negligible enough that I wouldn’t bother getting rid of the K&N that is already on my car. OTOH, the K&N flows slightly better, but not enough to justify purchasing one. Others bring up good points about having a well-sealed air box. Mine, for example, had a number of obvious leaks, as do most others I’d wager. The air box is one of those items on the 928 that really falls short of what should have been fitted to such an expensive car (the instrument cluster is another example that comes to mind). It is really flimsy, subject to cracking, and being installed or assembled improperly. The rubber strap design is just pitiful.

At first I didn’t really understand the point of Roger’s new air filter system, but now I’m starting to see the light

Bill Ball

I just can't get around the greatly reduced surface area of the K&N. Bothers me. The K&N relies on some porous cotton with sticky goo to try to trap matter and still flow despite low surface area.

Maleficio

Is that setup available for the 16V?

VehiGAZ

I won't use a K&N anymore after one fried the MAF in my old Isuzu in 6 weeks. Maybe I over-oiled it, but whatevs - I had to pay $200 for a reman'd MAF from AutoZone. It's just not worth it...

YMMV, but that's my experience and my decision.

mark kibort

Bill, the porosity, not the surface area is the key to flow. the valleys of the KN are wider and will draw the most flow at that point. the KN overall, is MUCH more porous! It will absolutely flow much more than the paper filter, at a cost of possibly less filtering. If you want to use the KN and reduce the risk of MAF damage, oil lightly, ONLY one side (the outside) and wipe off any excess. been doing this for 10 years with the same MAF in racing and street environments.

M. Requin

I use a K&N because I live on a very dusty gravel road, and paper filters would be a whopping great expense, since I would have to change them so often. I've been using K&N and other oiled filters for 30+ years now, starting with bikes (not my old Thruxton, though - it had an Amal GP with a horn big enough to suck in a fair sized bird, or a section of my leathers, from time to time), and Mark is right, they work great unless they are over oiled. K&N recommends oiling the outside only - the hard part is deciding when enough is enough. My advice is that less is more. YMMV. And as noted, fit is critical. I have a very hard time fitting the K&N into the air box, it appears to be a little oversize, and it takes a lot of effort to get it in with a good seal. I think this is a manufacturing error on K&N's part.

James Bailey

Thus far no one has actually determined that an over oiled K and N killed their mass air.....known fact mass air sensors fail...they still fail with a k and N . They do not however show any increase in horsepower so the benefit is they can be cleaned oiled and reused. I do not run one but would if I had one for free

Maleficio

Regarding surface area, my 83 Audi 4000 CS Quattro used a fairly large air filter, but it seemed that air preferred to pass through a small spot about the diameter of a soda can, though the filter was sized like a shoebox. I'd just flip the filter around once in a while to allow the airflow to pass through a semi-clean spot. To think that air passes through the entire surface of an air filter is wrong. Air flow pressure concentrates in a small spot, like water draining out of a tub.

I think that large filters are a waste of material. And the 928 air filter is the largest I've ever seen.

mark kibort

this is easy to see. good point, but there is an easy way to prove this. because I run at dirty tracks so often, i can see the flow patterns by the dirt left in the filter. Actually the flow is very distributed because it comes from the sides. when I opened out the rear of the air box, the center area of the filter became more concentrated. the other reason the filter is wider, is that there is a certain amount of benefit to a larger air box as well. the nice thing about cleaning the cotton based filter often, with some oiling, is that you can see the flow patterns. air moves to differential pressure and the lowest pressure is at the MAF entrance. the gradients are spread out, in both directions to the air inlets, and rearward in my case, due to my rear vents.

mk

mark kibort

yes, there is a benefit in HP and it is measureable. I cant find the dyno I did when I did the test many years ago, but it was around 4-5hp. most of the tests that we have seen hear have been flawed with air box sealing inconsistancy. this would provide little if any gains when a change of filter was tested. I agree, the benefits are really the ability to clean and reuse them.

Ill do a dyno run with and without when I go and do the GTS class testing this summer. I have a sealed air box, so it will be a valid test.

mk

Dennis Wilson

If you use it on a CIS system, occasionally pull the lower filter housing and clean the air sensor plate. This should keep it from affecting the A/F ratio.

Dennis

F18Rep

I love these threads, second only to Dilbert. ;] Bruce

Iwanna928

I just ordered one, a K&N for my 79. It is a 79 so from what I have read not a big deal.

I don't like the OEM ones especially for my model. Seems way to restrictive when they get dirty and it didn't seem to clean well. Probably did it wrong.

I am going to dyno tune my car again next week to get the afr down to 12.5. See if the filter makes a difference too.