Thanks to a large amount of misinformation, and a lack of factual knowledge in the community at large, we decided to do a little experiment to determine which had the best manufacturing qualities.

Prior to this experiment, the only information I had to go on was hearsay, and this led to some conclusions that turned out to be incorrect. Some forum goers had indicated that the Porsche filter was labeled "Made in U.S.A.", and was assembled by Purolator (A MANN company). This may or may not be true, however, the logical leap was to assume the Purolator assembled filter was relabeled a MANN product. This experiment will preclude those former notions without fail.

First, we began with the three filters; A MANN filter, a Porsche OEM filter, and a Mahle filter all numbered 99310720303.
(These filters will always be pictured from left to right in this order.)







As you can see from the pictures above, the MANN and Mahle have a similar outward appearance, while the Porsche filter is evidently different. The dimpled canister, as shown in the third picture, combined with a more substantial thread and cap set it apart as incongruous.

The next step in the process was to put each filter on a lathe to properly cut them apart for internal analysis.



Again, it is the Porsche filter that appears different, and again, the MANN and Mahle filters appear of the same manufacture.





This exploded view shows that the primary differences between OEM and aftermarket are internal.



The Porsche branded filter canister itself you can rapidly see a lower pleat count, which would flow slightly less volume, and filter slightly worse. The two aftermarket units have a higher surface area with which to filter, and would, in a perfect world, filter better for a longer period of time.



The bypass spring is, again, clearly different in the Porsche filter. Again, this one appears slightly worse. The flat spring, while cost efficient, and capable, can be temperamental. If overextended, for example, in a high pressure situation, the spring can simply fail and allow oil to flow through the canister for the rest of it's use life. A coil spring, like the one used in either of the two aftermarket filters, would rebound to a useable position after the high pressure event had passed.



Most striking of all, however, is the anti-drainback valve. This valve is surprisingly non-existent in the Mahle or MANN branded filters.





In the canister design itself, the Porsche unit uses a slightly thinner wall, yet the threaded end of the cap shows a higher thread count, and may encourage better thread engagement. In addition, the threaded cap of the housing is more substantial, and would be less prone to bending if overtightened.

Our numerical findings are as follows:

Housing Length:
Porsche - 98.6mm
MANN - 99.8mm
Mahle - 99.5mm

Housing Outside Diameter:
Porsche - 76.4mm
MANN - 76.1mm
Mahle - 76.1mm

Filter Cartridge Height:
Porsche - 75.7mm
MANN - 76.1mm
Mahle - 76.4mm

Filter Cartridge Outside Diameter:
Porsche - 68.0mm
MANN - 68.4mm
Mahle - 69.1mm

Number of Filter Pleats
Porsche - 45
MANN - 67
Mahle - 66

You may come to your own conclusions, however I will voice my own as well.

First, I feel that the Porsche filter provides sub-standard filtering and high pressure protection. With the high weight oils that some owners like to use, a pressure spike high enough to bend the spring would not be uncommon.

Second, the little rubber anti-drainback valve is the cause of your concern. Either of the aftermarket units will empty themselves of oil, which leaks back into the crankcase, seeps past the piston rings, and causes smoke on startup. The Porsche branded filter, alone among these three, will seal itself from any backward flow through the filter.

In the meantime, MANN filter 99310720303 has been removed from our site until we can come up with a solution to the start-smoke issue with this filter. The small MANN filter has also been removed from each of our 993 service kits, and has been replaced with the Porsche branded filter at no additional cost to the end consumer.

If you have added an aftermarket anti-drainback valve exterior to the filter, you are in no danger of startup smoke.