K & N Air Filter?
There are several arguments against installing a K&N Air Filter:
1. The K&N doesn't filter fine particles of dirt as well as the stock air filter. (vaguely recall reading a Road and Track test of such filters and the difference was significant in the amount of dirt "caught"). One of the tests cited below says 18 times as many fine particles as other filters. Now why would you buy an air filter except to keep dirt out of the engine and prevent the wear it causes? This to me is the compelling argument and not the next one which is more often cited.
2. If not oiled properly and allowed to dry correctly, it can cause MAF fouling and the MAF is a $400 part. This can be reversed by cleaning the air intake passages between the filter and the MAF and cleaning the MAF. But often the resulting Check Engine Light drives the user to the dealers for some expensive service they wouldn't have needed otherwise. Correctly oiled and dried before insertion, this should not be a problem.
3. As the K&N is used for more and more miles, it gradually clogs faster than the stock OEM filters and toward the end of it life cycle, actually reduces air flow when compared to the stock air filter. So while it may give you more HP in the beginning of its life cycle, it gives you less in the end and the average is approximately the same. The K&N makes sense if you are using it in a racing situation where you are changing the oil and cleaning the filter frequently. Not much sense for an on-the-road use where the filter is expected to work for 15k miles or more.
4. Its use may cause problems with any warranty that is on the car. The dealer may insist on restoring the car to "stock" before working on it if the perceived problem could be in any way associated with the air/fuel mixture. And any major failure claim could be complicated by the installation of non-stock parts. Unlikely, yes. But can you afford to take the chance. On a well used '97 with little value and no warranty, this would be no issue.
Some additional reading
and read the rest of the links on the above page
read the 3rd paragraph of the summary on the above page
Now go here and you won't use the thing.
http://www.amsoil.com/video/company/EaFilters/index.aspx (2-3 minute videos (5 icons) that demonstate filter performance)
http://www.synpsg.com/uploads/g2202_Ea_Filters.pdf (Oil Filter/Air Filter Comparison - Good media efficiency comparison from paper to wet gauze type filters)
Mike Focke's Index of Boxster Web Pages
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