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Does CAI really work?

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JimC

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Discussion starter · #1 ·
With my old carbed trucks, this was a no brainer. The cold air, a denser air charge, made the engine run better. The less dense the charge, the worse it ran. Now comes fuel injection and we seem to think the same thing applies, but hold on. This year NASCAR ran FI for the first time. We expected colder temps would make the engines run better, but..........something new entered the picture. The on board computer, which no matter what the air density is, it still maintains a 14.7 to 1 ratio, thereby making the density of the air coming in of no importance. By the way, NASCAR found the cars actually used more fuel in the cooler temps (denser air). Go figure. I could be totally wrong, but this is food for thought.

Jim
 
#2 ·
Finally, somebody with conclusions similar to mine.
CAI is for all practical purposes a waste of money if the car had a reasonably well designed low restriction intake system to begin with. It's also a misnomer if you look at the 'standard' cone filter installations, which pull air from all sides of the cone, not from the front of the vehicle as in most factory installations.

On the denser air front, I've charted the fuel mileage on one of my vehicles for over 100,000 miles and nearly 300 tanks of fuel. I then broke it down by driving season - Fall/Spring, Summer, and Winter. All have similar peak MPG in the 27-28 range, and all have similar minimum in the 19-20 MPG range, but by far the most and best MPG occurs in spring and fall with moderate temperatures and no AC demand. Winter is several MPG lower on average and the colder it is, the worse the mileage. I ran a tank in -5 weather, all highway and only got 21-22 while the car routinely averages over 25 in the summer. Summer mileage is in the middle, but when I could run without AC, it was by far the best mpg.
My old S10 was the same way (1986 Iron Duke). Summer 30 mpg day in, day out. Winter 25 mpg. I have about 250,000 miles of MPG numbers on it.
 
#3 · (Edited)
One of the big problems with most of these so called CAI systems is they plop a cone filter under the hood turning it into a “hot air intake”. . .

On my old Jeep I “upgraded” to the K&N ”FPIK” and while it sounded really good it hurt my mpg and made my Jeep feel like a dog on hot days (I also ran an AMSOIL air filter because K&N is junk!) My stock air box had a scoop on it that poked in front of the radiator to gather fresh air not heated by the motor and radiator, I never did put the stock air box back on because I liked the sound too much.

On my Dodge I went ahead and kept the stock air box but I took a few of the intake pieces of my Camaro project and replaced the ribbed intake boot with smooth pipe but kept the stock air box, It sounds great but haven’t noticed a change in mpg or anything else. I prefer the stock air filter over the cone style because they filter better and you can get them anywhere.

There was a post I can’t find anymore but someone did a test. Took a temp probe and placed it in the stock intake setup and went for a drive and recorded the temp, I believe the temps where just a few degrees above ambient for the most part. Then they ran the same test again with the “CAI” and temps where significantly higher. The hotter the air the thinner it gets the less fuel the computer adds. . .

There are some true CAI systems out there that will help more so than hurt you just have to be aware of which those are. My K&N FIPK was a terrible design, the heat shield did next to nothing when it came to keeping the filter away from sucking the radiating heat. The bottom of the heat shield had a 2” gap all the way around the bottom and let heat radiate into the filter location, it also did not have a barrier to keep it from sucking air from behind the radiator.

I’m willing to bet most of the gains people see are from replacement of an old dirty filter and system designed to keep noise down with a much thinner filter and free flowing system with more surface area, not necessarily the denser air charge. Think of it as a vacuum, it has to work to bring the air in, the easier it gets air the better it runs, that's why I force air into my Camaro:D. . .
 
#4 ·
Good points on the K&N vs other 'cheap' paper elements - I've seen more than one set of tests that proved the AC Delco air filter was better at filtering and had less restriction than all the other products tested.
All filter designs are tradeoffs between filtering efficiency and pressure drop. Guaranteed that most 'High Flow' filters give up filtering efficiency, which you'll eventually see in liner and ring wear....
 
#5 ·
One thing you are not taking into account with the "denser" air from a CAI and it's effect on performance with a cmputer controlled car. The only time the PCM is managing the fuel system to maintain the 14.7:1 a/f ratio is in closed loop operation which is basically "normal" driving on the highway or streets after the vehicle has warmed up. At WOT, which is really when you are trying to get the best performance, the PCM defaults to a preset fuel map that only takes into account intake air temp, coolant temp, TPS, and MAP sensor readings. It does not look at O2 sensor readings which is the only way it knows what the A/F ratio is to adjust anything. So a denser cooler air charge will make more power than a hot air charge under open loop operation at WOT, but not in normal closed loop operation. Which is why if you go to the drag strip your truck will be faster with a cool engine on a cool night than in the middle of the day during the summer with a hot engine.

So the answer is YES a CAI does work. And as mentioned most of the "CAI" sold are not true cold air intakes. As they leave the filter unprotected under the hood. But that really only makes a difference at low speeds or in stop and go traffic. On the freeway there is enough airflow through the engine that it will be no different on the intake temps than with the stock airbox. Especially if you remove the rubber flap next to radiator.
 
#6 ·
One thing you are not taking into account with the "denser" air from a CAI and it's effect on performance with a cmputer controlled car. The only time the PCM is managing the fuel system to maintain the 14.7:1 a/f ratio is in closed loop operation which is basically "normal" driving on the highway or streets after the vehicle has warmed up. At WOT, which is really when you are trying to get the best performance, the PCM defaults to a preset fuel map that only takes into account intake air temp, coolant temp, TPS, and MAP sensor readings. It does not look at O2 sensor readings which is the only way it knows what the A/F ratio is to adjust anything. So a denser cooler air charge will make more power than a hot air charge under open loop operation at WOT, but not in normal closed loop operation. Which is why if you go to the drag strip your truck will be faster with a cool engine on a cool night than in the middle of the day during the summer with a hot engine.

So the answer is YES a CAI does work. And as mentioned most of the "CAI" sold are not true cold air intakes. As they leave the filter unprotected under the hood. But that really only makes a difference at low speeds or in stop and go traffic. On the freeway there is enough airflow through the engine that it will be no different on the intake temps than with the stock airbox. Especially if you remove the rubber flap next to radiator.
 
#8 ·
I have a scangauge, which monitors a bunch of different things, including air intake temps, ambient air temps, intake manifold pressure-vac.

I made a home built cold air intake and placed a cone filter all the way inside the passenger fender hole.

Ambient temps and intake temps were about the same, but I read up to -0.8 in-hg of vac at certain rpms during a WOT run. Mind you, the intake I created had 2 90degree bends on top of the 90 degree bend near the throttle body. As well, the inner fender is stock. I could have added a few holes on the bottom end of the inner fender to promote airflow, but decided to leave all that stuff alone.

So I took the CAI and placed the filter right at the plastic elbow on the stock intake tubing. Vac is now at - 0.1 at WOT and intake temps are about 3-4 degrees above ambient.

The only time intake temps climb, is when the truck idles for 3-4 minutes. At that point, it can hit 100-100 degress farenheit. It takes a couple of minutes of driving for intake temps to drop slowly.

IMO, I dont think there is much of an advantage to a CAI unless you live in a very warm climate on a very hot day.
 
#9 ·
Dual Ram Air / Cold Air netted me fastest light mod of the year over on DRTC. I actually have the same mods otherwise, crappy shorty headers, and a heavier truck than most and I ran 275 tires on the front as well. It works plain and simple. The colder the air, the denser... it makes horsepower provided the WOT air fuel is in check. Why do you think there are intercoolers and water / methanol / alcohol injection for boosted aplications? And blacksrt4 is right about alot of bends in your intake system being a bad thing! It eventually adds up to slight restriction. Now if the difference in air temperature between ones "cold air setup" and a cone filter in the engine bay is only 10-20 degrees then there wouldnt be a very noticable difference provided restriction is measured the same.... But there WOULD be a difference none the less. The more of a temperature reduction the better if you are looking to squeeze every last ounce of power out of a setup.
 
Discussion starter · #11 ·
If you take the computer out, it will seem to run better, but optimum fuel economy and power is a known value that has been available to us for years through literally thousands of dyno runs. That is 14.7 to 1 A/F ratio. Any variation from that loses power and economy. Let's not talk about altitude, because that adds another dimension to the whole thing.
 
#12 ·
The magical 14.7 number is actually driven by the EPA and the catalyst game. Best economy comes from lean burn, best power comes from slightly rich burn. The emissions problem is that that ugly NOX thing shows up at the higher combustion temperatures that are usually associated with lean burn.
 
#13 ·
JimC said:
With the intake air temp being taken, the computer does map according to the predetermined mapping in the computer. So basically the computer ends up with a 14.7 to 1 A/F ratio.
Click to expand...
Not true. The PCM runs rich at WOT to be "safe" and not damage the motor. And if you have a custom tune you can change the WOT fuel tables to tweak the A/F ratio. My truck runs about 12.5:1 at WOT with the custom SCT tune. On the Mopar PCM it was closer to 11:1. And before I had the SCT tune tweaked it was hitting 10.5:1. All WOT a/f ratios read using a AEM wideband guage. Which pretty much matched the A/F ratios on the dyno runs I had.

And as mentioned, the 14.7 A/F ratio thing is more for the EPA than anything.
 
#14 ·
It may or may not benefit my engine, but it something nice to look at under my hood.

Image


:D
 
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#15 ·
So I've skimmed through most of what has been added to this and haven't seen this in any of the responses.
We all agree that colder air is denser. So logically, if you have .50lbs of air at 70*F it will take up less volume than .50lbs of air at 150*F.
Our combustion chambers have a fixed volume, so, because colder air takes up less volume per pound than warmer air you can put more pound of cold air in the combustion chamber than you can of Hot air.
Well all know that an engines power relates directly to how much air and fuel is can use. So, assuming the computer keeps the same a/f ration, 14.7:1, you will still be getting more lbs of air and fuel per combustion event due to the denser air. Remember a ratio is just a measure of one relative to the other. If you have more of each you cans till maintain the same relative ratio.
 
Discussion starter · #16 ·
Ultimately, the idea is to decide whether CAI is worth the money. If you are thinking with a 'carb mentality' (that's me), it is probably worth all the big bucks (they are not cheap). Thinking in a new way, with fuel injection, a CAI won't make a real noticeable difference. It all gets back to the thing that is at the center of it all, ECM. Instead of spending money on the intakes and all, buy a programmer or have your unit reflashed. You can adjust your A/F mixture to best suit your needs.

I am all for mpg and low end torque.

I heard one of the guys on "Horsepower" say it best,

Horsepower is how fast you go and torque is how quick you get there.
 
#17 ·
tell ya what how bout one of you guys find me a stock airbox filter and all and ill take my truck to a dyno then remove that piece of junk and try it with the intake I jus bought from nick and we can see whats better, hands down a CAI adds more power and air to your engine.
 
Discussion starter · #18 ·
One of the interesting things we don't realize is that an engine can only take in as much air as it's smallest restriction. (Not counting turbo and such) If the smallest restriction is the throttle body, it matters not how big the CAI or intake tube is, it won't take in any more air. That's physics. I have made an effort to measure the area of the intake tubes in my system. I had a question about the "air hat", so I put in a tube that is bigger than the throttle body. There is more than enough filter surface area to accommodate the intake (about 2.7 times throttle body area). Next is the air box itself. The intake nozzle is in question as it may actually be smaller than the throttle body. The answer would be to attach a 3" flange to the box and over the hole in the panel atop the fender and put in 3" tubing from the box to the panel. This eliminates the need for a CAI if you have restrictions in the system. And it is much cheaper than a CAI.
 
#19 ·
Interesting thread.
CAI will change the performance of the engine, what you want and what it changes however may be two different things.

1) It allows more air mass into the cylinder, that means more power.
2) It by virtue of (1) requires slightly less TB opening and since a petrol engine is more efficient at wider openings your engine will loose MPG slightly in most cases.
3) If you live in an extremely hot area and your driving involves a lot of hills, you may see improvements in economy due to the increase in power and engine efficiency being nearly the same for wider TB openings between standard and CAI systems.

Not really much more to it than that. If you want MPG increase, unless you are the exception to the rule, see (3), don't bother.
If you want more kW then go for it.

These apply to petrol vehicles.
Diesel is completely different but I've seen people conflating performance gains in diesel and projecting that onto petrol engines. They are two totally different combustion processes and behave radically differently.
 
#20 ·
Let's keep one thing firmly in mind.

The factory box? Is a CAI already (notice where it sucks the air from.)

Most CAIs? Are actually WAIs, and suck less dense warm under-hood air.

Why doesn't this show up on bench dynos? Because either way, you have cool air around the filter. Try checking on a rear wheel dyno during a hot day with the engine bay heatsoaked some day ...

Besides, only rarely is the intake at this point the choke point for the motor.

I WILL say that removing input noise silencers can yield some nice sound effects *grins* Also, it does pay to find a nice low-restriction air filter (I'm partial to Wix myself).

RwP
 
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