Four Different Air Filters that Fit the Stock Air Box?
by Blitzo


Intro:
There are two basic performance modifications that most Spyder owners don't even think twice about.  The first set is the air filter and the second is the exhaust.  The air filter is about the cheapest performance mod and often the first that performance minded owners undertake.  With the recent flood of AEM intake replacements, let us not forget about the venerable replacemnents that fit the stock air box - the TRD model 1 and 2, and the K&N.  I will outline the three options that currently exist on the market as well as one that is already discontinued, but you might still be able to find.

 

This is the factory original stock  filter element.
The Stock Air Filter:
 The filter that ALL of us have is the stock air filter that comes with the car.  The filter is a porous synthetic element (probably nylon) that is molded in a  rectangular carrier.  They are made in Japan by Denso, so they are true Toyota manufactured parts.  There are 26 folds yeilding a surface area of about 378 square inches.  The Toyota part number is 17801-16020
This is the first version of the TRD filter.
The TRD Non-Renewable Air Filter:
The only filter available for the first few months of the Spyder's introduction was the TRD replacement filter.  It is a very similar synthetic fiber weave filter material, but is a charcoal color and has a fiber weave like a window screen on the back side for reinforcement.  I cannot tell for sure, but this filter material seems to be slightly thinner than the stock filter, but the same material and density weave.  The plastic carrier is the identical moldings, so this part, too, is made by Denso in Japan.  The original price on this baby was well over $70, even from discount sources.  The discontinued part number was 17801-ZT300
This is the updated K&N renewable filter.
This is shows the dramatic difference in thickness of the K&N and the stock filters.
The Updated K&N Renewable Air Filter:
The second filter available after a few months of the Spyder's introduction was the K&N filter charger.  The original model, 33-2041 was quickly replaced by an updated 33-2041-1 which had a better fit than the original.  The cost on these run from $40-$50.  There is a separate filter recharging kit available to renew this filter for up to one million miles.  This is probably the most common replacement filter.  It has a cotton cloth filter element with a fiber screen backing on both sides and is molded in what appears to be a rubberized silicone rubber frame.  It has made in the USA molded into the frame.  The thickness of this element is significantly thinner than the stock filter, yielding a much smaller surface area.  There are 32 folds yielding only 221 square inches - over 40% less than stock or the TRD non-renewable version.  The smaller surface area comes from the thinner depth and slightly narrower elements because of the way the frame is molded.  With a smaller surface area, you would hope that the porosity of the filter element would provide for an improved flow through the filter.
This is the updated renewable TRD filter.
The Updated TRD Renewable Air Filter:
This is the second generation air filter available from TRD.  The price on this filter at about $40 is significantly lower than the original TRD unit.  There is a separate filter recharging kit available to renew this filter for the life of the car.  It was rumored that this was just a relabelled K&N unit.  There are enough differences that I'm not entirely sure I believe that anymore.  Surface area over 21 folds comes in at about 160 square inches - much less than ALL the others.  It makes you wonder if there is any performance difference over the original TRD unit.  It is nice to have a much cheaper filter that will last indefinitely, but does it perform as well?  Who knows.
You can see that the TRD and K&N renewable filters have a few differences.
Is the TRD Second Version the Same as the K&N Filter? - No:
I don't believe that the renewable TRD filter is made by K&N - there are too many differences.  I don't have a TRD renewable in my hands, so there are a few things I can't check, but there are alot of visual differences.  First, the filter material on the TRD is gray, not red.  This could just mean they use a different color oil than K&N, but it is still the K&N formulated oil.  The color differences in the moldings are also not very definitive - it is not hard to change the color of something.  But here is where the differences start to mount up.  

First, there are 32 folds in the K&N, and only 21 in the TRD.  Second, the lengthwise margin of the TRD is significantly thicker than the K&N.  Third, the K&N has 3/16" of the edge of the filter element encased in the molding material, where the TRD only has bleed-over.  Fourth, the lip on the short edge is short on the TRD and taller on the K&N.  All four of these things spell different mold, and different mold spells different manufacturer.  I believe that TRD did not outsource their filter manufacture to K&N, but decided to copy their design and have Denso manufacture it.
Conclusion:
Well, that pretty much sums up the cosmetic differences in the replaceable filter element choices for the Spyder.  What performance differences there may be are still unproven.  But that's another story....