by: Dean Lewellen

This month's article provides the opportunity to put together some perhaps interesting and informative bits and pieces of technical information that have collected in the "in basket" over the past several weeks but individually lack the magnitude needed to support a complete article.

First item--I came across this very innocent yet captivating sounding article titled, "Are Performance Air Filters a Good Idea?" This article was found on an Audi Club web site (www.norcalaudiclub.org), on Sean's A4 Page, and, was actually contributed by a well-known BMW tuner by the name of Jim Conforti whose web site is at Bonneville Motor Works. Enough for the credits, already. The article presented some independent test lab data generated by an unbiased, non-sponsored group evaluating a BMW M3 stock air filter and a replacement K&N air filter as the test subjects. The test procedure used a standardized "test dust", a precise method of "loading" the test dust on the filter faces, and measured both initial free and then loaded air flows and particle volume passing through the test filters. Both filters were the same size and fit the BMW M3 air box. The BMW filter had an effective filter area of 8.4 sq. ft. while the K&N filter had an effective area of 1.6 sq. ft. for a stock to replacement filter area ratio of 5.25:1. The stock BMW filter has more and deeper pleats than the K&N product. Filter efficiencies were measured for test dust loadings of zero and going up to about 40 grams/sq. ft. The K&N filter flowed better than the BMW filter at zero loadings by 8%, and, was better by about 1% at the 40 grams/sq.ft maximum dust loadings during this test. What gets your attention is the measurement of differential pressure across the filtering medium at constant airflow as both filters were dirtied (read loaded up with dust) at a test rate of 75 grams of dust in 20 minutes. This test is not unlike the environment our cars live in daily as we drive on the streets and roads here in Arizona and this is where the effective area of the test filter's surface really comes into play. Even though the BMW filter flows a bit less at the same loading, it loads up 5.25 times slower because of its larger effective area, therefore passing less dust particles into the cylinders. The bottom line--the K&N filter initially flows 8% better, but as the dust loads both filters' surface, the K&N filter begins to flow worse at a faster rate than the BMW filter because it loads up much quicker while passing more dust through, as well.

I measured and calculated the effective filter areas on two stock Porsche air filters and their K&N replacement counterparts for comparison with the above data. One pair was from a 1989 3.2 liter Carrera engine and the other pair was from a 1995 3.6 liter 993 engine. The 3.2 liter engine's stock filter had an effective area of 5.2 sq. ft. while its K&N replacement had an effective area of 1.3 sq. ft. for a stock to replacement filter area ratio of 4.0:1. The stock 3.6 liter engine's air filter measured 4.6 sq. ft. and its K&N replacement measured 1.9 sq. ft. for a stock to replacement filter area ratio of 2.4:1.

Whether or not more dust in the intake air charge actually causes long term problems is not documented or even speculated about. The next step would be to do this same type of independent comparison on a number of different engine pairs using both kinds of filters over an engine's lifetime and analyzing what is found inside. This is all becoming way too anal for most Porsche owners/drivers. All I know for sure is that I have replaced the K&N replacement air filters in my 993 and 740iL air boxes with the original paper parts since both of these cars live on the street everyday. The additional air flow allowed by the K&N products make sense for your Porsche on Driver's Ed track days but will not be felt during the weekday travel in your Porsche anyway.

Second item--Not to pick on K&N, their fine product line or their reputation for excellence, but, there have been some drivability issues in cars equipped with DME controls (all 1984 and later Porsche engines) that have been traced to the air mass flow sensor being contaminated from an excessively oiled K&N filter medium. I always have the problem, according to my better half, that if a little of something is good than a little more of it will be even greater! This is apparently not true when cleaning and re-oiling your K&N air filter's screen material. Go easy with the recharger oil as the instructions alert you to do when servicing your unit.

Third item--I received some very interesting tire usage and performance data from Roger Ellingson, Pacific Northwest Region member and PCA Protest Committee Chairman about the tire brands used in the 2002 Porsche Parade Autocross and the tire brands used by the class winners at the Parade Autocross this year. There are two sets of information to follow from which you can see the overall popularity with serious autocrossers of your favorite tire brand name and some measure of the performance of your favorite as well. The performance capabilities are greatly clouded by the capabilities and/or shortcomings of the unidentified vehicles and the unknown drivers, but the conclusions one can draw are several and fun.

Tire brands used in the 2002 Porsche Parade Autocross

Kumho 59
Hoosier 46
Bridgestone 42
Pirelli 32
Yokohama 30
BF Goodrich 25
Michelin 22
Goodyear 14
Continental 9
Dunlop 6
Toyo 6
Firestone 5 (really !)
Fulda 3
Sumitomo 2
Falken 1

Tire brands used by the class winners in the 2002 Porsche Parade Autocross

Hoosier 16
Kumho 13
Yokohama 9
BF Goodrich 6
Pirelli 4
Fulda 2
Goodyear 2
Michelin 2
Bridgestone 1
Falken 1

And the winners were--? Falken was 1 for 1; Dunlop was 0 for 6; are Hoosier equipped cars better prepared or are their drivers more skillful?; are Bridgestones really that awful?; I had better stop before I get in real trouble with someone. Enjoy and draw your own conclusions.

Product news--Porsche Cars North America news bits include the sales in North America for the fiscal year ending July 31, 2002, were 23,108 which is down from the 25,412 cars sold in the previous year. PCNA said that 12,620 Model 911s were sold in North America in 2002 which was 14.4% more 911 sales than in any previous fiscal year.

PCNA announced the price for the base Cayenne S at a MSRP of $55,900. and the base Cayenne Turbo will be offered at a MSRP of $88,900. The world's newest SUV goes on sale in Europe beginning December 7th and will be in North America dealers' showrooms early next year, 2003. Wow, ninety large for a Cayenne Turbo certainly represents rarified air for the price tag of any SUV that rolls its wheels anywhere on this planet! I saw a fleet of three Cayenne test mules or prototypes in late August heading North on the 101 bypass near Mesa one Friday afternoon. They all had Georgia Distributor plates and lots of blackout panels and graphic taping to disguise the truth--but they were real Cayennes and moving quickly but safely northward.

Finally, a tidbit some of you may not have heard about--Fred Schwab, CEO of PCNA, was chastised in public at the Cayenne press introduction in Leipzig, Germany, in late August by the good Dr. Wendelin Wiedeking, Porsche AG CEO, for offering the $500. and $1000. rebates/incentives to any PCA members purchasing 2001/2002 Boxster and 2002 Boxster S models before December 31, 2002. Schwab said the rebates meant "nothing" and they didn't really count as an incentive because they were limited exclusively to the Porsche Club. Hello!--Is anyone listening to anyone? The card I got in the mail describes the $500. and/or the $1000. as an "...incentive for the purchase of...". Gee, I wonder if my $100. discount card from PCA President, Bob Miller, for the purchase of Genuine Porsche parts, Tequipment and Selection merchandise purchased before year end is also under fire from the authorities in Stuttgart.

So long for this month--I have to get to the Porsche North Scottsdale parts counter before they close. Happy motoring!