the TRUTH about CAI (cold air intake)

[rebelbowtie]

i notice a lot of post on here about CAI much like any other forum, i have a little write up i like to post from time to time if you guys have a minute to read i can share my thoughts.

Have you purchased a cold air intake kit for your vehicle yet? If so, you are among the many thousands who (for various reasons) have bought into this technology. But does it really do what you thought it would?

The most common reasons people give for installing a Cold Air Intake are:

1.More Horsepower
2.Better Fuel Efficiency
More Horsepower! Now this one is true, but might be a little misleading. Cold air intakes can result in actual gains in power, but not necessarily in the way most people are expecting them. The key that is typically missing in the mind of the average consumer is that the only time power is increased is when the engine is at Wide Open Throttle (WOT). For those who don't know what that means, WOT is basically when the gas pedal is pressed all the way to the floor.

Some are now thinking "Wait a minute! The cold air intake lets cooler, more dense air into the engine. It also has less restriction than the stock setup. This lets it 'breathe' better, and therefore is more efficient." What can I say? You're right...at wide open throttle. What many people don't realize and what many others simply forget to consider is that there is a throttle valve connected to your gas pedal that is constantly restricting the air flow into the engine. The only time it is not restricting the airflow is when it is wide open...hence the term WOT. Some will now say "But it will still breathe more efficiently even at part throttle." You must then remember why there is a throttle valve in the intake to begin with. The throttle valve determines how much air enters the engine, and the engine computer (for fuel injected engines) determines how much fuel to mix with the air. Several factors influence how the computer determines this, but the result is basically the same: a fixed Air/Fuel Ratio will be supplied to the cylinders. This should be obvious since all modern vehicles have to comply with EPA emissions standards.

That means that more air = more fuel = more power = more speed. Now that's good if you're at WOT, but how many of you drive at WOT even 1% of the time? The fact is that you almost always drive in part throttle...because you're usually limiting the vehicle's acceleration. That is the key. Any time you limit vehicle's speed/acceleration with the gas pedal, you are actually limiting (restricting) the amount of air entering the engine. This defeats the purpose of the cold air intake, high-flow intake, high-flow filter, etc. It is only effective when you're at WOT.

One thing should be clarified here...when I refer to WOT, that can also be a little misleading. The condition where these devices increase power is not always exactly at WOT. The throttle valve on a car's intake system is typically a butterfly valve. The more it is closed, the more restrictive it becomes. The least restrictive condition is when it is wide open. Keep in mind that the intake system is sized to operate the engine through a full range of speeds and load conditions. If you get full power from your engine at 5,000 rpm, the throttle valve is sized allow air to flow through it at that speed. Now how much air do you suppose is flowing when you're only turning the engine at 2,500 rpm? This is the situation you have when your're pulling a heavy load (trailer, etc.) in a high gear. This is the situation I find myself in with my pickup when pulling a travel trailer. In 3rd gear at 60 mph, the intake manifold pressure and mass airflow don't change at all from about 70% open throttle to 100%. Why? The throttle valve is effectively at WOT for that speed. There is no measurable resistance being offered by the valve when at 70% open. Does that mean that a cold air intake would help when towing heavy loads? Probably not. The reason is that when you have the condition described above (you have more pedal, but it doesn't change anything), the intake system (filter & piping) is providing very little air resistance. You know this because the primary form of resistance--the throttle valve--isn't even doing anything from ~70% and up. That tells you that there is not as much air flowing through the intake as there would be at high rpm (like if you down-shifted), and therefore your air filter creates a very small amount of resistance by comparison. NOTE: This is assuming that the air filter is clean. If it is clogged up, that's a different story.

In summary, the cold air intakes and high-performance filters are good for improving full-pedal engine power. Practically that means that you are buying a modification that helps you pass (at full-pedal) or race. Don't expect fuel economy gains…sorry.

 

[Bennythbeaver]

it's all about air density. cooler air is more dense!

 

[rebelbowtie]

The factory intake is already cooler than the ambient temps inside the engine bay. You won't get a much cooler charge without meth/water or an intercoooler. Or maybe sitting bags of ice on top of your intake...you can try and disprove this post but these aftermarket "CAI" are only good at WOT and marginal at best. 110% waste of money on a stock engine

 

[Mr. Banks]

Re: Cai

I bought into this. The only thing I gained was an AMAZING combination of Volant CAI and Borla Dual Exhaust growl paired up together for an awesome sound.

My HCF deleted stock airbox is back in with a K&N drop-in reusable filter. The sound alone wasn't enough for me to continue to use the CAI.

 

[fun_runner]

Maybe I'm the odd ball here. Bone stock, I got 20.5mpg on the hiway. After an Injen CAI, Airaid throttle body spacer, and custom catback with Borla Pro XS single in, dual out mufler, I now get 22.4 one the hiway. Maybe the intake by itself does nothing since the stock exhaust would still be restrictive? Idk. I do know for a fact that my mileage increased with the mods I've done. I check my mileage every time I fill up. I also drive like an old man 95% of the time. I'm sure that helps too.

 

[rebelbowtie]

Throttle body spacer on a modern EFI engine is also another product that's not worth anything. On a TBI or carb a spacer helps atomize the fuel mixture but not with our 4Runner engines

 

[fun_runner]

I know. It was on the clearance rack at Summit Racing for $15. It was an impulse purchase. Its red so it matches a few other little things under the hood. :shrug:

 

[ALBPM]

Maybe I'm the odd ball here. Bone stock, I got 20.5mpg on the hiway. After an Injen CAI, Airaid throttle body spacer, and custom catback with Borla Pro XS single in, dual out mufler, I now get 22.4 one the hiway. Maybe the intake by itself does nothing since the stock exhaust would still be restrictive? Idk. I do know for a fact that my mileage increased with the mods I've done. I check my mileage every time I fill up. I also drive like an old man 95% of the time. I'm sure that helps too.

I went the same route almost - an Injen intake with the new dry Amsoil filter and a Borla XR-1 muffler. I got back the gas mileage I lost when I went from 265 tires to 285/75/16. I have a 20 mile drive to work in mixed city and higway and I average 21-22 MPG. And I don't drive slow - typically 5-10 mph over the speed limit.

 

[KidVermicious]

Rebel is exactly right. This tendency to call anything with a cone filter a "Cold Air Intake" drives me up a freakin' wall. There's nothing "cold" about the air under the hood, no matter what filter you're using.

High flow filters and ram air intakes can give horsepower gains as part of a balanced system (IE, in combination with things like a custom cam, free-flowing exhaust and fuel management mods). They don't do much by themselves, for exactly the reasons Rebel stated. A bigger funnel does you no good if the neck is the same size.

If you want quick performance gains, they're in your exhaust header and muffler.

 

[ALBPM]

I'm doing better with the Injen than the Stock AirBox and the ISR mod. I'm also getting better mileage with E weight 285s that the Stock Air Box and 265 tires.

Also, here's a good thread about Intake Air temps.

http://www.toyota-4runner.org/3rd-gen-t4rs/108171-scangauge-ii-owners-intake-air-temps.html

Seems the Injen stays cooler than most CAIs because it's longer and extends past the radiator.

 

[jam46283]

This sounds good in theory.. Although the entire paragraph is arguing against a cai letting More air in.. The purpose of a cold air intake is Not to let more air total.. (Hence argument about only gaining at "wot"). But it is to let cooler denser air from outside the engine bay in, thus improving the power output.. I don't see how you're making the claim it only does anything when you're flooring it? :? Altho I do agree they are misleading when people think it will be a huge gain

 

[Zumie]

I threw a COBB CAI on my Subaru and I notice a SERIOUS gain in throttle response.. It was insane how much better the engine responded. So I guess what I'm saying is that it isn't all about HP and MPG...

That thing sounds amazing too. CAI on a turbo engine sounds gooood.

Cleans up the engine bay, sounds good... If you MPG and HP increase that is for sure a bonus.

 

[OrdnanceMarine]

An intake needs to be tuned for the application you're using it in and is part of your overall tuning setup. While some vehicles can see a small improvement with a specific intake alone, others will actually see degradation in performance, especially if the intake is affecting the air/fuel management. I have a decent amount of experience tuning the K20Z3 motor (2006-2011 Honda Civic Si) and if you just slap an aftermarket intake on and call it good you will generally mess with your air/fuel ratios and end up with some weird throttle response issues since you've affected the way the air flows over the mass airflow sensor (most of us tune with the MAF disabled). In these cases if you haven't tuned the ECU to compensate for these changes and you are seeing a true increase in fuel economy then you're almost certainly running lean and on an engine that puts out 70lbft/liter in stock form and 90lbft/liter with simple bolt-ons and tuning, and you're asking for problems. We don’t have those kinds of outputs in these engines so it is probably harder to hurt the engine by blindly slapping on an aftermarket intake but I still don’t think it is a good idea regardless.
That being said, I don't know where the bottlenecks are on these engines. I have a feeling the header is the #1 offender. Personally I'm not at all concerned with the power output at 3500 RPM and above as I rarely see those kinds of engine speeds in my Runner. What I want is more power in the 1000-3000 RPM range where I do my daily driving and even towing at.

 

[Merle]

Used to muck w/ this stuff when I had a Supra but times pass... As do memories

CAI intakes were great when we were trying to make speed and times at WOT. The turbos, the intercooler and generally the entire engine bay were a massive heat sink which restricted how much air we could get into the engine. Devices like a turbo helped "suck" more air into the engine (and the engine was simply a massive air pump), and ice around the intercooler (water spray, alcohol combo) helped increase the air density.

But with those engines, it boiled down to getting as much air into the engine so the larger injectors and fuel maps could combine it at the right ratio in order to increase horse power.

With the 4Runner, it'd be different. The air/fuel mix is pretty good (constant) for whatever RPM you're at. Increasing the air density doesn't mean you have more air coming into the engine IF the throttle body is partially closed restricting that air.

The mass air flow sensors generally reads not only the amount of air coming through (fixed diameter, measures flow speed) but also the density of the air (temperature gauge). So the MAF knows exactly how much air is incoming.

Again, if your throttle body (butterfly plate?) is wide open and you are still not getting enough air because of whatever restriction - then yes, CAI will help. But if it's at 50-80%, CAI won't do a thing as the MAF is telling the system how much air is coming in and the system is accommodating the overal ratio of A/F mix.

Too much air is bad. You run too lean, burn the rings and fry your engine. A little lean is good as that's where you're close to your max HP/Torque. Too rich is a safety valve as it only costs fuel.

Way back when we'd wire in potentiometers (aka resistors) to our MAF in order to tell the system it was warmer than it was in order to allow more air in. There's a limit as you do start to reduce the life of your engine (but hey, the Toyota Supra engines are/were bullet proof).

Am I off, is my memory that shot?

 

[V8.]

Used to muck w/ this stuff when I had a Supra but times pass... As do memories

CAI intakes were great when we were trying to make speed and times at WOT. The turbos, the intercooler and generally the entire engine bay were a massive heat sink which restricted how much air we could get into the engine. Devices like a turbo helped "suck" more air into the engine (and the engine was simply a massive air pump), and ice around the intercooler (water spray, alcohol combo) helped increase the air density.

But with those engines, it boiled down to getting as much air into the engine so the larger injectors and fuel maps could combine it at the right ratio in order to increase horse power.

With the 4Runner, it'd be different. The air/fuel mix is pretty good (constant) for whatever RPM you're at. Increasing the air density doesn't mean you have more air coming into the engine IF the throttle body is partially closed restricting that air.

The mass air flow sensors generally reads not only the amount of air coming through (fixed diameter, measures flow speed) but also the density of the air (temperature gauge). So the MAF knows exactly how much air is incoming.

Again, if your throttle body (butterfly plate?) is wide open and you are still not getting enough air because of whatever restriction - then yes, CAI will help. But if it's at 50-80%, CAI won't do a thing as the MAF is telling the system how much air is coming in and the system is accommodating the overal ratio of A/F mix.

Too much air is bad. You run too lean, burn the rings and fry your engine. A little lean is good as that's where you're close to your max HP/Torque. Too rich is a safety valve as it only costs fuel.

Way back when we'd wire in potentiometers (aka resistors) to our MAF in order to tell the system it was warmer than it was in order to allow more air in. There's a limit as you do start to reduce the life of your engine (but hey, the Toyota Supra engines are/were bullet proof).

Am I off, is my memory that shot?

Solid post.

So i guess the only benefit of a CAI is the sound...

 

[WillK]

An intake needs to be tuned for the application you're using it in and is part of your overall tuning setup. While some vehicles can see a small improvement with a specific intake alone, others will actually see degradation in performance, especially if the intake is affecting the air/fuel management. I have a decent amount of experience tuning the K20Z3 motor (2006-2011 Honda Civic Si) and if you just slap an aftermarket intake on and call it good you will generally mess with your air/fuel ratios and end up with some weird throttle response issues since you've affected the way the air flows over the mass airflow sensor (most of us tune with the MAF disabled). In these cases if you haven't tuned the ECU to compensate for these changes and you are seeing a true increase in fuel economy then you're almost certainly running lean and on an engine that puts out 70lbft/liter in stock form and 90lbft/liter with simple bolt-ons and tuning, and you're asking for problems. We don’t have those kinds of outputs in these engines so it is probably harder to hurt the engine by blindly slapping on an aftermarket intake but I still don’t think it is a good idea regardless.
That being said, I don't know where the bottlenecks are on these engines. I have a feeling the header is the #1 offender. Personally I'm not at all concerned with the power output at 3500 RPM and above as I rarely see those kinds of engine speeds in my Runner. What I want is more power in the 1000-3000 RPM range where I do my daily driving and even towing at.

This says it all. Are there benefits to adding an aftermarket intake- yes, but minimal. Add an exhaust with the intake and you'll increase that benefit. Tune for that intake and exhaust and you'll get maximum benefit.

I spent many Saturdays and dollars getting cars tuned based on bolt-ons (and some internal mods- heads, cam, etc..) and I can speak from proven data that bolt-ons do help.

But, simply spending $300 to $600.00 (I'm assuming cost- I haven't bought any in years) doesn't automatically guarantee a return for your money. Again, there are quality vs. junk intakes and exhaust.
I once added an Amsoil air filter, a $50.00 muffler and a slight timing advance to a vehicle and saw and 11 HP and 17 TQ increase, with a 2MPG increase over stock. Again, the HP/TQ numbers showed up over stock numbers (baseline). And other's in our group added an expensive exhaust and intake and saw literally the same increase numbers over stock.

Generally, users will see better throttle response and improved MPG, which in the end makes them happy, which is all that matters.

 

[aika1]

i notice a lot of post on here about CAI much like any other forum, i have a little write up i like to post from time to time if you guys have a minute to read i can share my thoughts.

Maybe it's my science background, but this post irks me. There's not a single reference or a shred of evidence in the post. And the assertion that a cold air intake only works at wide open throttle is laughable as well- K&N has actual graphs that show an increase in horsepower along the power curve (torque too). Is it huge? Nah. But it's there. Do cold air intakes work? Yeah, they do. But they're not forced induction; they are a modest gain. But a 5% gain in horsepower ain't so bad really... Especially not for a bolt-on...

Disclaimer: I don't have a CAI on my 4runner. I merely saw this post and was unimpressed by the lack of a foundation to the argument...

 

[Jmdwifi]

Maybe it's my science background, but this post irks me. There's not a single reference or a shred of evidence in the post. And the assertion that a cold air intake only works at wide open throttle is laughable as well- K&N has actual graphs that show an increase in horsepower along the power curve (torque too). Is it huge? Nah. But it's there. Do cold air intakes work? Yeah, they do. But they're not forced induction; they are a modest gain. But a 5% gain in horsepower ain't so bad really... Especially not for a bolt-on...

Disclaimer: I don't have a CAI on my 4runner. I merely saw this post and was unimpressed by the lack of a foundation to the argument...

I put one on my FJ and the TRD exhaust. I got back my 1 mile per gallon that I lost when I went to 285's but it was less responsive taking off. WOT was much more dramatic. That may have had to do with the sound but it did feel a little more peppy wide open. All in all it was a waste of 700.00 for the CAI and Exhaust. My exhaust tip on this 4runner looks just as good. The rest of my truck, well, not so much.

 

[Aelfwine]

Maybe if you just throw out your dirty one and put a new stock filter in instead of a CAI, you'll feel the little difference as well? Just sayin'...

 

[rhobere]

not quite...

I'm not a very active member here and I never post so I doubt anyone will take me seriously (not to mention I'm bringing a post about a very tired subject back from the dead, sorry google brought me here), but I'm also a mechanical engineer with research in thermal fluid systems and I have a lot of background with pneumatic systems and pump design.

So here goes...
I don't disagree at all with the methodology and thought process you're using, but you're not getting at the whole picture with your analysis and came to the wrong conculsion. Your conclusion that the amount of power you get doesn't change unless at full throttle is for the most part correct. You will see minor changes at partial throttle just due to different flow characteristics, but they will be small. Unless tuned properly, those changes could even be negative. However, your conclusion that they don't get better efficiency unless at full throttle is completely wrong.

The cylinder is acting as a linear pump on the intake stroke. If you're running at, for example, 3000 rpm, your engine is having to pump about 75 liters of air per second which is not negligible. That's quite a bit of air to move.

NOW, to your point, whether you have an intake or not, the throttle will control the flow of air to the engine and you will be using 75 L/s either way. But the point of a CAI is not to increase air flow. Its to decrease the amount of work the pump (cylinder) has to do to move 75 L/s of air. It does this by reducing the amount of head loss in the flow between the inlet and the throttle body. This is Pump Design 101. If you want to increase the efficiency of your pump, you should first decrease the head loss at your inlets and outlets.

Head loss is just fluid dynamics jargon for power needed to overcome friction/resistance in a pipe. Head loss increases as the length of the pipe increases, as the diameter of the pipe decreases, or as the pipe changes shape, bends in any way, or even changes diameters. If you didn't notice, all of those things: changes in shape, changes in diameter, bends; they all exist inside the air box that sits between the inlet and the air filter AND between the air filter and the throttle body. Removing all of that and installing a CAI shortens the length of the pipe, usually increases the diameter, and generally follows a much straighter/smoother path all with the goal of decreasing head loss.

The result is that your engine will not need to produce as much work to pump the air it needs to run. That is why so many people claim to see an increase in fuel efficiency. Not because of an increase in air flow, but from a decrease in the amount of resistance there is to that flow.