[war damn brz]

I recently received a Perrin filter (CAI filter, not the panel filter) from a family member that didn't know that there was more to replace to be able to install it. So, I got to thinking of ways to use this filter with little or no modification to the stock intake system, given how efficient it performs already. Cut me some slack because I have not investigated this far and I am just looking for more perspective of the idea:

For visualization, here are some links to pictures of the filter and the air box:

Filter
http://perrinperformance.com/images/M93106101

Airbox
http://www.drivingenthusiast.net/sec-blog/wp-content/gallery/2012-12-02-cars-and-coffee-austin/img_2519.jpg

I am thinking since the end of the Perrin filter has a silicon fitting, it might be possible to fit it inside of the stock intake box by fitting the silicon end into the stock box's exit hole. Since the stock intake piping is a smaller diameter than Perrin filters', some cuts may need to be made into the silicon to allow a flush fit. The filter will be a snug fit into the box, but it should be able to fit as long as you push it far enough into the box's exit hole.

So that's the rough idea, obviously there would be precautions taken to make sure the fit is air tight.

Let me know if more clarification is needed.

So let's hear some opinions. I want as many criticisms and skepticisms as I can get before I jump in and ruin a good filter.


Thanks Everyone

 

[Subieman]

The problem I see is poor airflow. The round filter will end up so close to the inside of the air box that airflow would be reduced.

The main reason for factory air box design is reduction of noise. The main addition of an aftermarket air filter with no box is noise which makes the engine sound more powerful but isn't.

Pleated paper filter elements have very low resistance to airflow because the pleats increase the surface area subject to the pressure difference substantially reducing the resistance to airflow. Also, they last a long time between replacement for the same reason.

The aftermarket "low resistance" air filters work by not filtering as efficiently. I'd be very, very surprised if these filters show any meaningful increase in airflow on these engines which are pretty much detonation limited anyway. If you also change the intake and exhaust piping and manifolds then maybe a larger filter box and element might be useful but for the stock engine the stock filter should be fine.

 

[war damn brz]

Thanks for your input Subieman. I figured there would be restricted airflow where the end of the filter meets the inside of the box's exit hole, but have thought of ways to reduce this.

But from what you're saying, even if I successfully mount the end of the filter inside the intake box's exit hole with little or no restriction to air flow, there would still be airflow restriction from the filter being inside the box?

What would you think about removing half of the box and simply using the other half to mount the filter?

 

[Subieman]

Yes, the proximity of the box to the filter surface is what I see as the restriction.

The box is designed to accept a flat pleated paper filter. Lots of space above and below to allow the pleated filter total area to accept airflow.

These aftermarket filters take the box off which eliminates losses from noise reduction. They rely on free flowing air around the outside of the filter to gain their claim to low restriction flow. Putting a box around these free flow filters defeats the purpose.

 

[war damn brz]

Definitely taking a different route, thanks.

The box is designed to accept a flat pleated paper filter. Lots of space above and below to allow the pleated filter total area to accept airflow.

I'm currently a Mech. Eng. student and just out of curiosity why would a larger surface area filter be better, would that not mean more restriction?

 

[Subieman]

Definitely taking a different route, thanks.



I'm currently a Mech. Eng. student and just out of curiosity why would a larger surface area filter be better, would that not mean more restriction?

Think of the pleated paper filter flattened out in an airbox big enough to hold it. Imagine every hole in the paper filter as leaking air no matter what angle each hole presents to the airflow. If you pleat the paper you can fit way more holes in the filter. The holes in a paper filter are very small but there's a lot of them. Even K&N know to fit pleated filters and their claim to fame is actually washable filters rather than low restriction. They claim only "1-4 hp gains" apparently regardless of engine size which tells you a lot. Nobody can feel 1-4 hp on any engine big enough to drive a car!

As you know, flow through the obstruction is proportional to the pressure differential driving the flow and the restriction presented to the airflow. When the objective is to reduce the pressure drop to a minimum (getting that driving force as low as possible) then you need as much filter area as possible to deliver the volume. Pleating the filter provides the necessary area but squeezes it down into a manageable size.

Low restriction filters using oiled foam filter medium have very low filtration area and clog up quickly. They also operate at higher air speeds through the filter medium making much more noise. Filter manufacturers make pleated paper filters because they have been proven to work best for street applications where very high mileages are expected from the engines protected by the filters. Foam filters are actually bad news for long life street engines. Paper filters are now so effective they are replaced very infrequently and no servicing is required between replacements.