the TRUTH about CAI (cold air intake)

[IBallEngineer]

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.

OK, you understand air flow, I get it. But I think the OP has a better grip on this situation than you do. As you very accurately stated above, improperly tuned the changes could be negative. I would argue almost none, and quite possibly all, of the aftermarket intakes are never actually tuned. In addition even if they were tuned, it's doubtful the end user has the same set up as the lab "tuned" engine. AND more importantly, the pump is only as efficient as the entirety of it's capability. This means head loss at the outlet negates whatever minuscule gains are achieved in the intake. K&N dyno charts are just that, K&N's charts, intended to sell. I do agree the efficiency can be positively impacted by a good intake, I DO NOT believe slapping a pretty intake on is going to give you a 5% power increase and 10% mileage increase. That is just not going to happen.

I'm still glad you posted this, your insight is very welcome here. Hope I didn't offend too badly!

opcorn:

 

[ben550]

K&N is desperately trying to delete this thread... haha bad for their business.

I've never wasted money on aftermarket "cold" air intake systems. I try to not lose sight of the fact that I am driving a truck to the dog park, not a nascar in the Daytona 500...

 

[rhobere]

OK, you understand air flow, I get it. But I think the OP has a better grip on this situation than you do. As you very accurately stated above, improperly tuned the changes could be negative. I would argue almost none, and quite possibly all, of the aftermarket intakes are never actually tuned. In addition even if they were tuned, it's doubtful the end user has the same set up as the lab "tuned" engine. AND more importantly, the pump is only as efficient as the entirety of it's capability. This means head loss at the outlet negates whatever minuscule gains are achieved in the intake. K&N dyno charts are just that, K&N's charts, intended to sell. I do agree the efficiency can be positively impacted by a good intake, I DO NOT believe slapping a pretty intake on is going to give you a 5% power increase and 10% mileage increase. That is just not going to happen.

I'm still glad you posted this, your insight is very welcome here. Hope I didn't offend too badly!

opcorn:

I'm definitely not trying to imply that intakes are worth their money with that post and I'm definitely not trying to say that the OPs general conclusion is wrong. My opinion based on personal experience is really that it depends on the car as I've had cars that saw significant improvements in mpg and negligible or even negative changes (until I tuned them).

I'm simply trying to explain that flow rate is definitely not the only thing that dictates power or efficiency and that, at least in theory, intakes definitely do increase power and/or improve efficiency. I said that because, even if his conclusion that intakes are useless without a tune is usually true, OPs analysis was fundamentally flawed from the beginning and ignored pretty basic principles in engine design.

However, the point you made (that I bolded) is not actually true. A system's efficiency, ignoring the thermodynamic efficiency, is a function of head loss and head loss is the sum of the losses in the entire piping network. The performance at the inlet and outlet are completely independent of each other. On top of that, the losses in the exhaust system are generally not that much bigger than the losses in the intake system, believe it or not. Most of the difference comes from the catalytic convert and the fact that the gases are moving faster, but the difference is smaller than you would think.

 

[TheWraith]

certain designs have gains in different parts of the power band...

Longer tubed or a True CAI have a mid to hi torque power band than the short CAI. I learn this with playing with a few designs on some of my street cars.

Short Ram Intakes made good top end power. But when I added my extension to my short ram and made it into a true CAI which draws cold air by the front air dam ... It made more mid end power than top end... And I've seen it on the dyno ...

but for me a cold air intake or the TRD one I'm looking to get and mating to a ARB Snorkel should work the same was as a cai and a ram air...

 

[Scramble]

I have the 2.7L with a 5 speed so I'm at WOT A LOT! It sounds like a CAI would be good for my truck. I also live in a very hilly area.

 

[OrdnanceMarine]

As an engineer who's worked from the aero side AND hands on with tuning smaller displacement auto engines (mostly the incredible K20Z3 engine that came with the previous generation Civic Si) I can say that you can assume NOTHING about changing the induction system in any way! You HAVE to test it. The myriad of variables are so incredible that you could spend dozens of hours modeling a setup but you'd still have to validate by actually building it and testing it and even then, if you have good models, they were built upon lessons learned by actual testing. (Stomping my foot three times) you CANNOT make assumptions when it comes to intakes. You HAVE to tune them and any changes to the length, size, shape, restriction, etc. of the induction system can play all kinds of games with the results. With the 4Runner we've got a relatively low output engine for it's displacement so there's a good deal of safety margin between the ECU's ability to adjust short and long term fuel trims so you're likely not going to cause any harm by running a modified induction system but you're also not going to unlock any magical MPG or power improvements and any improvements would need close calibrated study to even be able to prove. I'd love to have a tuning solution for these Toyota engines or at least the ability to datalog what's really going on but I don't know about anything that exists.

 

[popsmckracken]

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.

I don't know how old this thread is but I noticed today while changing fluids my 96 was idling very low, when I opened the top of the air filter box it picked up and seemed to run more efficiently. I have a high-flow K and N filter installed in the box but just opening the box made a noticeable difference. I DO NOT have a CAI because of what I have heard so many times about what a waste it seems to be....but that big stupid plastic box cannot be an asset. I'm not into paying for something that HAS GOT to be easy enough to do DIY. ANyone have success with deleting the restrictive box and replacing it with something DIY. I mean a cold air intake is a shiny tube with a filter on it for 250.00.....no thanks. Someone must have a system design that works as a less constrictive intake?

 

[MonsterMaxx]

for those of you who have tried a CAI and gone back to stock...anyone want to sell their CAI?

 

[rcebowl]

i going to go ahead and agree to disagree with the OP.

a couple of points.. i'm not good at explaining things im a little too ADD and tired soo just spitting balling thoughts

1) IMO there is NO WAY you can say without a doubt that EVERY coldair intake doesnt provide more power. Weather limited to a TB or not.. increased VE through the piping is still increasing VE. there can be other limits besides the TB. Coming from the import car world, i'll give you a perfect example. The Evolution 8/9 had a lower Intercooler piping that had a massive taper to like 1.75 inch, when replaced and (no tuning or anything else) you could massive gains in spool, hp, on and off WOT, there are maps to proof this if I have to find them. VE can still change on an off WOT.

2a) but to the OP's point NOT ALL coldair intakes do make power, and sometimes they make power where you dont want it. this is VERY true for trucks where we are rarely use the top 85% of our rpm band. example using the the B16A2 motor found in the Honda SI from 99-00 cold air intakes made more PEAK power but a short ram intake made more power across the entire power range.

2b) The point of a cold air intake is that it draws "fresh air from the outside" but understand that once you "draw" all the "hot" air out of an engine bay it gets replaced with outside "cool" air so even then it would happen a fast enough rate it wouldn't/shouldn't matter. (so when you look at certain cold air designed and draws from both inside engine bay and outside engine bay it can still be "cold air".
Here's cool comparison from a BMW aftermarket company, their stock ecu have the ability to read air temps so it's an amazing comparison.
N54Tech.com - Your Source for International Turbo BMW Racing Discussion - View Single Post - DCI Hot Air Myth Testing
proving that "hot" air really isn't THAT big of a deal. (and that's from a twin turbo inline6 not a small little n/a 4 cyc that doesn't produce much heat).

3) Dyno test are not a fair test for any intake system really. many Car intakes are designed to work with air actually going through them, and if there is no air flow they do not work as they are designed. so you aren't testing them at their true efficiency

4) many intakes for car produce power because of MAF adjustments. Example Subaru WRX. many of the aftermarket intakes produce power bc they actually trick the MAF by taking reading at a different spot than a OE maf placement would (like in the tube) this causes the AF/Rs to lean out which helps produce power. This isn't a HUGE deal (depending on who you ask) bc OE turbo charged cars are pretttty rich to begin with. although on the wrx there are lean places in the curve some most people tell you too tune rather than not. At which point some of the intake produce no (peak) power gains at all to very min power gains....

4b) but that's looking at PEAK power which is different than under curve. which brings a WHOLE OTHER fruit basket. I'd take a intake that gave me zero peak hp difference as long as it change my entire tq curve (under peak). (which can't really happen but just stating a if the option were there).


again... might be rambling I hope some of this makes sense.. or i guess i should say you can make sense OF it.

I'll end with again.. i know...there is no apples and oranges here.. its just facts across different car designs. So that said... do what YOU want, after all it's YOUR car/truck.

 

[rcebowl]

5) the OP stated that just bc you gained power doesn't mean you'll gain efficiency.

That's a bs statement. IF the tq was only changed at the top 2000 rpm FINE it's a true statement. IF the entire tq shifted up, you WOULD gain mpgs. Also it's common knowledge that maintaining rpm isn't what kills mph it's getting to speed. IF it's easier for your car to get to speed AND if it can maintain a certain speed at a lower rpm BC it's making more power than you would again get mpgs

More often than not more power means more mph IF your taking about the same motor/tranny/tire combo. (again you could make statement false if you would like, you can make any statement true as well) In this case making it true is WAY easier than false.


6) some people argue that the only reason some intake make power is bc you are using a less efficient filter (referring to it's main job of cleaning air). The most efficient of a filter more slows down air, the LESS efficient of a filter the faster air passes making more power. so some people say you make more bc of that. I believe this to be true ... so from the OP point sure i'll take that. But i'll also state.. who cares.. we are taking about DUST from this point. any dust going through a filter will burn up ... or get clogged in the oil that in your air from your blowby system. (which should be clean from time to time anyway. Clean you MAFs too people!) so like who care if your intake a little dirtier... or you suck up a little more dust if you're gaining power and mpgs. =P


7) many motors are limited BEFORE the TB ... that head design will limit way more than TB or intake system.. chew on that for a bit =P


8) a good question that's asked by a few car people is if the OE (or aftermarket) intake have a velocity stack designed into it? if the OE has a velocity stack built it.. maybe just a filter change is needed. if it doesn't... i feel every intake should...some cone filters have VS built in. I pretty much wouldn't get an intake without.


9) I will say I understand the want (different from need) of a heat shield. but like pending design might be needed might not be.

i'm sure i have more... but I keep forgetting my points.. sorry.

 

[Paddo]

Since someone else already resurrected this thread... What about replacing the stock intake to make more room (for a second battery, for example) in the engine bay? That filter box is pretty large.

It sounds like the general consensus is at least that it wouldn't negatively affect performance.

 

[mattkc16]

Hey Guys,

Im a new member to the forum and am having major powerloss @ the engine. I'm not able to post a new thread, so im replying to this one to see if you can help. I took my 5th gen to the dealership (twice), and to a second mechanic and they haven't be able to nail down the issue. Currently the engine is operating at about 30% power, they checked clogged cats, mass air flow sensor, fuel pressure. They are thinking the knock sensor is causing the engine to pull timing, hence the lost of power. they did check the sensor and wiring harness and both have good continuity (i.e. no issues with them) They didn't identify any knock or issue with the engine, but are recommending disassembly of the engine for a inspection to see if there are any issues $$$. Does anyone have any recommendations of other things to check, or any applicable threads?

 

[Wags1968]

I read all these posts (reread some) and my conclusion is....
We all need a CAI because there is ALOT of HOT AIR blowing around this thread LOL...

 

[A2toHgt]

Done correctly, they can add some gains. Done incorrectly, which is most of the time, they are worse than stock

 

[ToyoNation]

Minimal Gains

As with any cold intake, the gains are over rated and minimal. Yes the temp of the air is relatively the same regardless of which intake you are using, but the small gains are from a decrease in the air restriction. the smooth intake tubing and open cone filters help improve air flow. this is only my humble opinion. oh yeah and they sound cool. worth the cost? thats up to the driver.

thoughts?

 

[ToyoNation]

done correctly, they can add some gains. Done incorrectly, which is most of the time, they are worse than stock

this.

 

[krelnydelnky]

I’m thinking of doing one just to relocate the intake out of the wheelwell. Just did some long travel shenanigans and inner fender. (Till I make one which is not that easy!) so that intake cup is exposed = not good. So that’s my reasoning

 

[tb-av]

Not sure about all the variables but I had my 100,000 mile Limited for several months and drove it rather cautiously. New vehicle, totally different from what I was used to driving.

Now I drive a bit more 'normal' I suppose you could say.

Before my CAI I noticed my mileage was ever so slightly declining around a general point. After several months with the CAI, I noticed it increasing.

I have seen about .3 - .5 MPG increase. Now is it my driving, I would think that would have the opposite impact but who knows. Gas changes by season?

Higher tire air pressure? Could be many things but I did start to notice the reversal of the decline right after installing it.

So maybe they don't do anything except in very specific situations, but they don't seem to hurt matters and might just be able to get you up to a 1/3mpg more on long term averages.

That's been my unscientific subjective biased findings.

 

[HelpfulHindle]

Response to Your Write-Up

Your write up wasn't bad, but saying a CAI and throttle body spacer is a waste of money is a statement of your opinion. This thread makes you look like you're just trying to argue with people.

 

[alexfrankbob]

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...

Not only that but if people are like me, who had their last car for 14 years small gains, such as MPG over a long period can add up.