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I thought I would share this with the group. I did a project on my 90 Si 4ws last weekend, I built a new air filter element. Let me tell you my line of thinking to get to this project.

My goal is to keep this car relatively stock, at least in appearance while making small upgrades to optimize it's performance and reliability. I love it when I show people the engine compartment and they see a stock, unmolested car. No day glo wires, shiny ram intakes, etc. It is pretty rare to see such a clean car of this age that has not been assaulted.

As far as filtration goes, stock paper filters do a much better job filtering small particles over gauze type elements (K&N, etc.). So much better that I refuse to run a K&N. But, K&N's and other quality filters of this type do flow much better than paper, especially at higher RPM's. So what to do???

I was cleaning the foam filter out of my KTM and it hit me, a foam filter element.... Off road vehicles from dirt bikes, to quads, to trophy trucks all favor foam type elements for their superior filtration, excellent flow properties and ease of cleaning/care. So I went to work.

I hacked a stock paper filter for my car, removing the paper element from the perforated metal core that supports it. I purchased some UNI universal filter foam that comes in a sheet ($16). I cut it to fit and wrapped it around the perforated core, gluing the seam with gel type super glue. I then oiled it with my favorite filter oil, No Toil, and installed it in the factory filter housing. I previously removed the factory small snorkel that runs up across the top of the radiator and replaced it with an accordion style air tube that plugs into the cold air feed of the passenger headlight assembly. To the unknowing eye, it looks factory.

Results. The car seems to be a bit quicker responding to throttle inputs and it also seems to pull a bit harder up higher in the rpm range. I do not know if a dyno would actually show any improvement, but it did not hurt at all. Next time it needs cleaning, it will pay for itself by not having to purchase a replacement.

Just a fun DIY that worked pretty well and took me about an hour.
 

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Good for you, there are many ways to do a air filter setup.
And unless you are looking for more power air filters make no power, just better throttle response and more engine noise.

Real power comes from cams, port n polish, higher compression pistongs, bigger bore, then adding a better true cold air filter, and better aftermarket header or intake throttle Bodies with a chipped and tuned ECU to match for NA.

Or

Turbo charging.

Or

Motor swapping.

These motors are good for what they are and as with somethings, every little bit does help, but I would have worked on the other stuff before an air intake.

But good for you.
 

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Discussion Starter #3
Thanks for the comment. To clarify, I did not do it to increase performance (much), but to make what was there the best it could be without huge changes. You are right, without huge mods like forced induction, these cars will never be powerful. But, optimizing what is there can make small gains in drive ability and economy. Technology has moved a long ways in the 25 years since my car was made. Can I put some of those advancements into my car? Rhetorical question.... As an engineer and long time motorsports enthusiast, it is fun for me to try.
 

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Nice job, but this thread is useless without pictures. :troll:
 

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We do love pics! I would like to see some engine bay shots and a few pictures of the filter after modification
 

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In some cases a upgraded intake doesn't help at all and the stock design is actually better. Mcm did a test on a skyline and did a upgraded one and one that even stuck out the bay and still didn't help the oem one made the most power. It could help in this case that the oem design stays and it just flows better with a better filter. But like everyone says you won't tell if it really makes power unless you dyno. I changed mine and it made a difference but I think because the filter was just dirty and hasn't been changed.
 

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In some cases a upgraded intake doesn't help at all and the stock design is actually better. Mcm did a test on a skyline and did a upgraded one and one that even stuck out the bay and still didn't help the oem one made the most power. It could help in this case that the oem design stays and it just flows better with a better filter. But like everyone says you won't tell if it really makes power unless you dyno. I changed mine and it made a difference but I think because the filter was just dirty and hasn't been changed.
Depends on the stock design, whether you tune after installing the new intake, and where you're looking to make power (e.g. whether you go for a longer CAI or a well placed short ram). It is true however, that on a lot of newer performance oriented cars that the stock intake design is already quite good.

I forgot where I found the article but it was a pretty in-depth breakdown of why foam filters flow better than gauze type. I've got a Trust AirINX that I plan to install once I get new piping made up and I'll see how that goes.
 
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