Disclaimer: This is info I gathered and some of it may be my personal opinion...in no way intended to be all-knowing fact or infallible. Do your homework, read what's presented, and make your own informed decision.
The question is frequently asked: "Do cold air intakes make a difference?", whether this be improving gas mileage or improving performance.
the simple answer is NO. If you're interested why, read further.
A Problem:
ISO Coarse Dust Test of multiple brands of air filters - K&N clog faster and passes 3-4x more dust than paper filter:ISO 5011 Air Filter Test Report
They state: "Compared to the AC Delco air filter, the "K&N" plugged up nearly 3 times faster, passed 18 times more dirt and captured 37% less dirt."
Fine dust passing through a "K&N" in the stock TJ airbox:
How good are K&N filters?
Why does this matter? Dust = silica. Read about silica here:
Recognizing the Signs and Symptoms of Silica Contamination from Practicing Oil Analysis Magazine, January 2006.
The UOA (used oil analysis) with observed silica content in street driven vehicles:
Threw away K&N's due to high silicon in UOA's - Bob Is The Oil Guy
Cold Air Intake Design:
There are three main types:
1. Stock intake tube cut with a "K&N" cone style filter from local autoparts store clamped on the end.
2. An aftermarket tube, usually larger in diameter than stock, with a "K&N" cone style filter clamped onto it. Many utilize a 'heat' shield, and some utilize a "dry" filter instead of the "oiled" types.
3. Other intake options use a snorkel of some type, to draw air from outside the engine compartment (covered later).
Performance Gains:
Here is a dyno test performed by JP Magazine:
Jeep Wrangler TJ Inktake Dyno - A Day On the Dyno - Jp Magazine
Notice they showed a gain of 6 hp and 4 lb-ft of torque at around 4500rpm.
Here's a link to a 18 comprehensive dyno runs comparing the stock intake, no intake at all and an aftermarket cowl intake.
http://www.tricktuners.com/forums/showthread.php?t=226
He saw absolutely no statistically significant difference between the runs. And to actually show how easy it is to skew a dyno, he saw a near 10 hp increase just by changing tire pressure.
Have you ever wondered what the Jeep Engineer's would have to say about the stock intake vs a CAI?
well, read about that here: JeepEngineers on Cold Air Intakes.
So What Do We Know about Cold Air Intakes:
Pros:
1. Eliminates stock airbox (may be necessary for custom fenders)
2. Improved HP and TQ by about 2-3% at ~4500rpm (Engine max: 5200rpm).
Cons:
1. Expensive - brand name kits cost around $150+
2. Cleaning - open element filter is exposed to much more dirt, mud, dust and debris from engine compartment.
3. Thin film of dust typically passing through filter, thus the engine is exposed to this dust.
4. Oiled filter versions further attract dust, dirt and debris.
5. Due to inadequete filtering, a Outwears Pre-filter, or similar filter sock is required, further adding to cost.
6. Requires frequent cleaning due to dirty environment - typical cleaning kit costs $20+.
7. Increases risk of hydrolocking - exposed element can suck water into engine easily.
8. Noise - annoying "sucking" noise can be heard, sometimes associated with a loud whistle.
9. Dirty filter can cause rough and/or high idle.
I used to run an AEM intake, but removed it after finding a lot of problems associated with it. I documented my observations here: AEM Intake observations
The Snorkel:
There are also many brands of snorkels, designed to prevent water from getting into the engine, and to introduce air from outside the engine compartment. Brands include ARB, Volant, and others. Many people construct their own snorkel systems using PVC pipe and 1990's Buick intake boxes.
Pros:
1. Introduces air from outside the engine compartment
2. Elevated air intake to resist hydrolocking engine during deep water crossings.
Cons:
1. Expensive - ARB, Volant, etc brand intakes cost over $300.
2. Most require extensive modifications to the stock airbox, or a new airbox.
3. Modifications often require drilling and cutting of the body - could lead to rust, or water leaks.
4. Often times the windshield cannot be folded down.
Alternative DIY & Snorkel Write ups:
Buick/Hummer snorkel #1: TJ Hummer Intake Write-up (Buick Airbox)
Buick/Hummer snorkel #2: Write-up for a Hummer cold air intake
Low buck Buick airbox: Buick Airbox instalation
Homemade Cowl CAI #1: My Final Word On Cold Air Intakes
Homemade Cowl CAI #2: Cowl Induction - snorkle (WRITE UP)
Another cowl intake: Cowl Induction - snorkle (WRITE UP) - Page 4
Autozone Cowl intake: http://www.jeepforum.com/forum/f9/cold-air-intake-860538/
Buick airbox mounted directly to the throttle body: http://www.jeepforum.com/forum/f9/i-am-liberated-863818/
Homemade snorkel with K&N: http://www.jeepforum.com/forum/f9/homemade-snorkel-intake-w-pics-910113/
My personal favorites:
Windstar Airbox Cowl Intake: http://www.jeepforum.com/forum/f9/cowl-intake-windstar-air-box-566973/
Windstar Airbox Cowl Intake #2: http://www.jeepforum.com/forum/f9/windstar-cowl-intake-1064377/
Mustang Air box CAI: Mustang GT Air Cannister
Homemade Aluminum Snorkel: homebrew aluminum snorkel
Fun video:
The question is frequently asked: "Do cold air intakes make a difference?", whether this be improving gas mileage or improving performance.
the simple answer is NO. If you're interested why, read further.
A Problem:
ISO Coarse Dust Test of multiple brands of air filters - K&N clog faster and passes 3-4x more dust than paper filter:ISO 5011 Air Filter Test Report
They state: "Compared to the AC Delco air filter, the "K&N" plugged up nearly 3 times faster, passed 18 times more dirt and captured 37% less dirt."
Fine dust passing through a "K&N" in the stock TJ airbox:
How good are K&N filters?
Why does this matter? Dust = silica. Read about silica here:
Recognizing the Signs and Symptoms of Silica Contamination from Practicing Oil Analysis Magazine, January 2006.
The UOA (used oil analysis) with observed silica content in street driven vehicles:
Threw away K&N's due to high silicon in UOA's - Bob Is The Oil Guy
Cold Air Intake Design:
There are three main types:
1. Stock intake tube cut with a "K&N" cone style filter from local autoparts store clamped on the end.
2. An aftermarket tube, usually larger in diameter than stock, with a "K&N" cone style filter clamped onto it. Many utilize a 'heat' shield, and some utilize a "dry" filter instead of the "oiled" types.
3. Other intake options use a snorkel of some type, to draw air from outside the engine compartment (covered later).
Performance Gains:
Here is a dyno test performed by JP Magazine:
Jeep Wrangler TJ Inktake Dyno - A Day On the Dyno - Jp Magazine
Notice they showed a gain of 6 hp and 4 lb-ft of torque at around 4500rpm.
Here's a link to a 18 comprehensive dyno runs comparing the stock intake, no intake at all and an aftermarket cowl intake.
http://www.tricktuners.com/forums/showthread.php?t=226
He saw absolutely no statistically significant difference between the runs. And to actually show how easy it is to skew a dyno, he saw a near 10 hp increase just by changing tire pressure.
Have you ever wondered what the Jeep Engineer's would have to say about the stock intake vs a CAI?
well, read about that here: JeepEngineers on Cold Air Intakes.
So What Do We Know about Cold Air Intakes:
Pros:
1. Eliminates stock airbox (may be necessary for custom fenders)
2. Improved HP and TQ by about 2-3% at ~4500rpm (Engine max: 5200rpm).
Cons:
1. Expensive - brand name kits cost around $150+
2. Cleaning - open element filter is exposed to much more dirt, mud, dust and debris from engine compartment.
3. Thin film of dust typically passing through filter, thus the engine is exposed to this dust.
4. Oiled filter versions further attract dust, dirt and debris.
5. Due to inadequete filtering, a Outwears Pre-filter, or similar filter sock is required, further adding to cost.
6. Requires frequent cleaning due to dirty environment - typical cleaning kit costs $20+.
7. Increases risk of hydrolocking - exposed element can suck water into engine easily.
8. Noise - annoying "sucking" noise can be heard, sometimes associated with a loud whistle.
9. Dirty filter can cause rough and/or high idle.
I used to run an AEM intake, but removed it after finding a lot of problems associated with it. I documented my observations here: AEM Intake observations
The Snorkel:
There are also many brands of snorkels, designed to prevent water from getting into the engine, and to introduce air from outside the engine compartment. Brands include ARB, Volant, and others. Many people construct their own snorkel systems using PVC pipe and 1990's Buick intake boxes.
Pros:
1. Introduces air from outside the engine compartment
2. Elevated air intake to resist hydrolocking engine during deep water crossings.
Cons:
1. Expensive - ARB, Volant, etc brand intakes cost over $300.
2. Most require extensive modifications to the stock airbox, or a new airbox.
3. Modifications often require drilling and cutting of the body - could lead to rust, or water leaks.
4. Often times the windshield cannot be folded down.
Alternative DIY & Snorkel Write ups:
Buick/Hummer snorkel #1: TJ Hummer Intake Write-up (Buick Airbox)
Buick/Hummer snorkel #2: Write-up for a Hummer cold air intake
Low buck Buick airbox: Buick Airbox instalation
Homemade Cowl CAI #1: My Final Word On Cold Air Intakes
Homemade Cowl CAI #2: Cowl Induction - snorkle (WRITE UP)
Another cowl intake: Cowl Induction - snorkle (WRITE UP) - Page 4
Autozone Cowl intake: http://www.jeepforum.com/forum/f9/cold-air-intake-860538/
Buick airbox mounted directly to the throttle body: http://www.jeepforum.com/forum/f9/i-am-liberated-863818/
Homemade snorkel with K&N: http://www.jeepforum.com/forum/f9/homemade-snorkel-intake-w-pics-910113/
My personal favorites:
Windstar Airbox Cowl Intake: http://www.jeepforum.com/forum/f9/cowl-intake-windstar-air-box-566973/
Windstar Airbox Cowl Intake #2: http://www.jeepforum.com/forum/f9/windstar-cowl-intake-1064377/
Mustang Air box CAI: Mustang GT Air Cannister
Homemade Aluminum Snorkel: homebrew aluminum snorkel
Fun video: