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."
There have been numerous articles all over the Internet showing fine dust passing through K&N air 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 filterclamped 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 enginecompartment (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 (the guys who designed the Jeep Wrangler) would have to say about the stock intake vs a CAI?
Here's a response to a question on the forum from one of the actual Jeep Engineers:
Question:
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.
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.
Fun video:
Cost Effectiveness:
$250 for a cold air intake system
- let's say this will get you 20,000 miles before requiring cleaning
$20 for cleaning kit
- this will get you about another 20,000 miles
In contrast, for the stock airbox:
paper filter cost from local auto parts store: ~$14
This means for the ~$250 the CAI cost, you could have bought 18 paper filters. Considering you can get about 6,000-9,000 miles from each paper filter, that means you could travel at least 108,000 miles on $250 of paper filters.
For the cost of one CAI, and one cleaning kit, used to travel approx. 40,000 miles, you could travel ~120,000 miles on paper air filters.
It is simply not cost effective for 3% in power gains @ 4500rpm to jeopardize your engines health, or to waste money on expensive filters mechanisms.
Volumetric Efficiency:
The argument is often made that more air = more fuel and therefore more power. Well, first you should probably know the air requirement of the engine, so you can actually determine if the air intake is somehow restrictive. Engine Air Flow requirements are measured in CFM (cubic feet per minute)
Calculating the CFM of air required for an engine is pretty simple.
CFM = (CID x RPM x VE)/3456
For our 4.0L (4.0L = 244 cubic inches displacement):
If we assume 100% efficiency: (244 cu-in) * (5200 RPM-redline) / 3456 = 367 CFM
...but unforunately our engines are nowhere near 100% efficient, 80-90% is more reasonable for a modern engine.
So, in reality we have: (244 cu-in) * (5200 RPM) * (.85) / 3456 = 312 CFM
Well, Four Wheeler magazine tested a stock throttle body and found it flowed 450 CFM! Obviously that's even more than an ideal, non-real-world 100% efficient 4.0L!
They also did some extensive flow testing with a 4.7L stroker, and found it only used 383 CFM!
Source: http://www.fourwheeler.com/how-to/engine/129-0712-2000-jeep-wrangler-40l-inline-6/
Now, let's work backwards and figure out how efficient their high performance 4.7L stroker was:
We have: (289 cu-in) * (5200 RPM) * (.88) / 3456 = 383 CFM
So with more displacement, higher compression ratio, a modified head, valve job, performance cam and some other work, they were able to acheive 88% efficiency in this context...yielding 225 hp @ 5k RPM & 280 ft-lbs @ 4k RPM, at the crank.
Now let's look at the numbers....their performance stroker yielded 35 hp/45 ft-lb gain over stock (~16% increase)....for a few grand.
Think about that next time you read an advertisement that suggests a given percentage increase in hp/tq.
Here's more tech & math if you're interested:
http://www.epi-eng.com/piston_engine_technology/volumetric_efficiency.htm
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."
There have been numerous articles all over the Internet showing fine dust passing through K&N air 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 filterclamped 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 enginecompartment (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 (the guys who designed the Jeep Wrangler) would have to say about the stock intake vs a CAI?
Here's a response to a question on the forum from one of the actual Jeep Engineers:
Question:
Answer:
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.
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.
Fun video:
Cost Effectiveness:
$250 for a cold air intake system
- let's say this will get you 20,000 miles before requiring cleaning
$20 for cleaning kit
- this will get you about another 20,000 miles
In contrast, for the stock airbox:
paper filter cost from local auto parts store: ~$14
This means for the ~$250 the CAI cost, you could have bought 18 paper filters. Considering you can get about 6,000-9,000 miles from each paper filter, that means you could travel at least 108,000 miles on $250 of paper filters.
For the cost of one CAI, and one cleaning kit, used to travel approx. 40,000 miles, you could travel ~120,000 miles on paper air filters.
It is simply not cost effective for 3% in power gains @ 4500rpm to jeopardize your engines health, or to waste money on expensive filters mechanisms.
Volumetric Efficiency:
The argument is often made that more air = more fuel and therefore more power. Well, first you should probably know the air requirement of the engine, so you can actually determine if the air intake is somehow restrictive. Engine Air Flow requirements are measured in CFM (cubic feet per minute)
Calculating the CFM of air required for an engine is pretty simple.
CFM = (CID x RPM x VE)/3456
For our 4.0L (4.0L = 244 cubic inches displacement):
If we assume 100% efficiency: (244 cu-in) * (5200 RPM-redline) / 3456 = 367 CFM
...but unforunately our engines are nowhere near 100% efficient, 80-90% is more reasonable for a modern engine.
So, in reality we have: (244 cu-in) * (5200 RPM) * (.85) / 3456 = 312 CFM
Well, Four Wheeler magazine tested a stock throttle body and found it flowed 450 CFM! Obviously that's even more than an ideal, non-real-world 100% efficient 4.0L!
They also did some extensive flow testing with a 4.7L stroker, and found it only used 383 CFM!
Source: http://www.fourwheeler.com/how-to/engine/129-0712-2000-jeep-wrangler-40l-inline-6/
Now, let's work backwards and figure out how efficient their high performance 4.7L stroker was:
We have: (289 cu-in) * (5200 RPM) * (.88) / 3456 = 383 CFM
So with more displacement, higher compression ratio, a modified head, valve job, performance cam and some other work, they were able to acheive 88% efficiency in this context...yielding 225 hp @ 5k RPM & 280 ft-lbs @ 4k RPM, at the crank.
Now let's look at the numbers....their performance stroker yielded 35 hp/45 ft-lb gain over stock (~16% increase)....for a few grand.
Think about that next time you read an advertisement that suggests a given percentage increase in hp/tq.
Here's more tech & math if you're interested:
http://www.epi-eng.com/piston_engine_technology/volumetric_efficiency.htm
