I considered this as well. I wrote to aFe and attach my question and their response:
"The only time you will see any engine air is at an idle. So you are under no throttle pressure so it really doesn't matter what type of air you burn. The only time it really matters is when you are under throttle pressure. When you are under throttle pressure is when you are moving. If you are moving you are forcing outside air into the engine compartment. The outside air is forcing the warm engine air out of the way and is inhaled by the filter to go into the engine. The extra air inlet is to allow more to reach the filter. If you close it you could lose some air flow.
Michael D. Cain
Customer Service Representative
Company: 951-493-7100
Direct line: 951-493-7115
Fax: 951-279-4056
Email:
mcain@afefilters.com
Web:
advanced Flow engineering (aFe) Air Filters & Intake Systems
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-----Original Message-----
From: Rick Franz [mailto:ricklake@verizon.net]
Sent: Friday, June 29, 2007 8:31 AM
To:
tech@afefilters.com
Subject: Toyota FJ aFe system...
Sirs,
I have installed an aFe CAI system in my FJ Cruiser and while I am happy with the performance, I am puzzled by the ‘extra’ hole in the filter chamber that allows engine bay air to enter the system. This hole would seem to ingest hotter air than the port into the fender, and I am wondering if I close this port off if it will have a detrimental impact on the units performance. Can you explain the need for this port and tell me if closing it would be a mistake?
Rick"
Frankly, I found their response a bit obtuse, and they did not answer my question. Certainly air a few degrees colder would be ever so slightly more dense and should impact performance, however, when talking to an engineer who understands these things, his feeling was that a ten degree difference would be negligible and since the fender intake hole is smaller than the plenum delivering air to the throttle body,there would be a reduction in max performance at higher throttle loads - climbing up mountains, etc.
Closing the hole for a snorkel is a must, obviously. The snorkel I am working on is a simple design that would close both intake holes and a 5" or 6" diameter snorkel pipe will come directly out of the the top of the air box, thru the cover plate and hood and extend up about 6" to 12" above the hood, (it will telescope about 5".) The pipe would have a flange mount on the hood and a swiveling intake snout at the top with a non-restricting rain trap. It would only work with CAI equipped engines.
And no, don't ask....no pictures or drawings until I get it fabbed and installed. It will not be widely available, but should be easily copied by any body shop with someone capable of fabbing in stainless.
R
Ligten up, it's the internet. 
"Sometimes, it is better to keep your mouth shut and be thought a fool, than to open it and remove all doubt."
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