Cold Air Intake Myth?

[Diego9777]

Hello everyone!

So today I was notified by my auto-shop teacher that cold air intakes actually do not gain power but just makes it unnecessary and says to keep the stock air intake box. He actually advocates keeping an engine all stock with no modifications because that is not what the ECU was tuned for nor was the engine made for those kinds of MODS. What is your opinion on this?

BTW, I have the following MODS to my Ka24de (came with these when I bought the car, I am not the one accountable for these modifications):
1) DC headers 4-2-1
2) Injen CAI
3) 5Zigen Border III Cat Back Exhaust.

My other questions:
1) Is it worth having these MODS on my car?
2) What Modifications are actually useful for a stock engine like my ka24de?

I appreciate any help, thank you very much! :drool:

[MrSanchez925]

installing a Cold air intake give you barely any gains on its own.

its more of eye candy.

Having your set up frees up flow, and Does increase horse power (very little).
With a tune, you'd be able to squeze out a bit more, but the increase in power wouldn't justify the price of a dyno tune.

[racepar1]

A quality intake will gain a small amount of horsepower. Combined with a header and exhaust it will gain enough horsepower to be worth mentioning. As stated an ECU tune will gain just a bit more. It really all depends on the engine. Some engines gain more than others with the addition of simple bolt-ons. Some engines you gain nothing, as stated by your "teacher". It seems to me that he is just not really a fan of modifying cars and his personal opinion is clouding his statement of the facts.

[Fuego]

I personally wouldn't spend money on an N/A KA, but that's me. I know some guys keep them N/A for whatever class they race in.

As far as your shop teacher goes, I agree with racepar. Cars have been modified since (as far as I know anyway) the old bootleggers, your teachers opinion is rather silly.

Also, you don't have to capitalize "mods."

[Diego9777]

Well thank you everyone and also he said that adding the mods could lead to an off balance of air flow causing the car to have higher air ratio than fuel and that can cause idling issues and such and to be honest it did freak me out that I have idling issues haha. My car has a good warm up and whatever but after driving it, rpms shoot down to 500-600 range and it sometimes stays stable at 700-800 but then at times it bounces up and down between 500-600.. Its bad to fix this through the throttle cable right? Possibly vacuum leak? EGR valve? Im not so knowledgable on this but I learned that issues with those things could lead an idle problem


Sent from my iPhone using Tapatalk

[Fuego]

He's your autoshop teacher and he doesn't know how a MAF works? Is this just a paint/body class?

[Diego9777]

No its an "automotive and transportation technology 1-2" class in high-school and I hope he does but I can conclude from the way you asked that he doesn't or he's just finding someway to bring down mods haha and he is a very old teacher.. Like a 65 year old haha


Sent from my iPhone using Tapatalk

[Kingtal0n]

coming to this place for this sort of advice after you just heard from an actual teacher in a school... :barf:


He is trying to steer you in the right direction, without giving you the nitty gritty details that would take five hundred hours of reading by yourself in a dark room.

To lightly glaze the subject, since I have 6 minutes,
1. your exhaust system should be as small diameter as possible to maintain exhaust gas velocity, while also being large enough to permit the highest flow-rate requirement of the engine at peak horsepower without allowing pressure to rise in such a way that it impedes the flow of the intake event.
The factory exhaust of the 240sx is adequate for up to about 280 Horsepower at sea level, and should not be changing by anyone using a naturally aspirated 4-cylinder such as the KA24DE or even an sr20det with a stock turbo for any reason.

2. The factory air box is designed to protect the engine, where, so called cold air intakes not so much. The paper filter is the best filter you can possibly use to protect the engine. K&N Style, and others, do filter well, many of them- but not quite as well as the factory style paper gaskets do. They are more restrictive when they get dirty, and like the exhaust example, impede the intake event as they become more filthy. "Cold Air Intake"- that term, on the other hand, can hold some meaning if it actually functions to bring in denser air from the outside, however, many engines are designed to operate with a fairly consistent temperature. For ex., when the factory tunes an engine, they know the vehicle will be in many different types of climates, it could be cold or hot outside. By making sure the air entering the engine has reached a certain temperature, they can more tightly control the conditions of combustion. If suddenly the temperature were to change, the fuel or timing maps will no longer be optimal.


So everything you instructor dude said is completely true.

[Fuego]

The KA uses (I believe anyway) what's called a hotwire MAF. I'm going to pull straight from wiki because I am too tired to break all this down.

"A hot wire mass airflow sensor determines the mass of air flowing into the engine’s air intake system. The theory of operation of the hot wire mass airflow sensor is similar to that of the hot wire anemometer (which determines air velocity). This is achieved by heating a wire suspended in the engine’s air stream, like a toaster wire, with either a constant voltage over the wire or a constant current through the wire. The wire's electrical resistance increases as the wire’s temperature increases, which varies the electrical current flowing through, or the voltage over the circuit, according to Ohm's law. When air flows past the wire, the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit or causing a smaller voltage drop over the wire. As more current flows, the wire’s temperature increases until the resistance reaches equilibrium again. The current or voltage drop is proportional to the mass of air flowing past the wire. The integrated electronic circuit converts the measurement into a calibrated signal which is sent to the ECU.

If air density increases due to pressure increase or temperature drop, but the air volume remains constant, the denser air will remove more heat from the wire indicating a higher mass airflow. Unlike the vane meter's paddle sensing element, the hot wire responds directly to air density. This sensor's capabilities are well suited to support the gasoline combustion process which fundamentally responds to air mass, not air volume. (See stoichiometry.)"

Basically your ECU will read the increased flow and colder/more dense air and adjust for it.

Edit: As long as you do need exceed the flow capabilities of your MAF (never going to happen with CAI and exhaust only) or your injectors/pump (never going to happen with CAI and exhaust only) you will be fine.

[Kingtal0n]

Basically your ECU will read the increased flow and colder/more dense air and adjust for it.



the problem is, sometimes the air is hotter but more dense (such as in turbocharger applications) and sometimes the air is colder but less dense (naturally aspirated while its cold outside) and the difference is that, while both situations may have equivalent mass of air entering the engine, for this example, the ignition timing points for best performance will be completely different. Furthermore, the factory fuel settings are conservative, and the farther you wander from the anticipated path, the more conservative the ECU will generally become, which means a worse brake specific fuel consumption, reduced power output, and other side effects like increased emissions and carbon deposits perhaps.

[Def]

the problem is, sometimes the air is hotter but more dense (such as in turbocharger applications) and sometimes the air is colder but less dense (naturally aspirated while its cold outside) and the difference is that, while both situations may have equivalent mass of air entering the engine, for this example, the ignition timing points for best performance will be completely different. Furthermore, the factory fuel settings are conservative, and the farther you wander from the anticipated path, the more conservative the ECU will generally become, which means a worse brake specific fuel consumption, reduced power output, and other side effects like increased emissions and carbon deposits perhaps.

True in theory, but you missed the practical application of tuning with a MAF. Anytime you add HP/flow to a "safe" tune, the ignition timing gets inherently safer assuming it was at max best torque before you added flow.

BSFC would only be very very slightly altered in open loop. It's going to probably be better in closed loop due to the higher pumping efficiency of the engine. And I don't mean within the margin of measurement uncertainty, I mean quite a decent jump in BSFC.


To the OP, bolt-ons are fine for your car. Not to knock your teacher too hard, but he's a high school teacher who probably isn't the most knowledgeable guy when it comes to internal combustion engine theory.

[Mikester]

Let me add a couple more cents to this...

1. Does your KA have a CAI or a short-ram? An actual CAI system puts the filter right in the air stream- usually with some cutting/welding. A short ram (which is prolly what you have) just gets rid of the plastic piping in favor of a larger-diameter, less curvy metal tube that does not compress... therefore providing better throttle response. Your ECU reads the MAFS signal and provides an A/F & timing output. Without changing the tune and adding an intake, you aren't really changing anything in terms of I/O; you are only changing the amount of airspace for something less restrictive.

2. Installing a header and a less restrictive exhaust is the same principle, but on the exhaust side. Better throttle response.

Adding a short ram and header/exhaust only makes it easier for the motor to breathe- It does not physically change the volume of air entering/exiting the system...

Example: I put a short ram and header on my DD (2004 Toyota Solara). First thing I noticed was a hair less torque down low, but MUCH better throttle response and better midrange power. Also, my fuel mileage jumped about 5mi per gallon. As far as any true power gains, I'd say this is negligible at best... But what I ended up; with is a car that breathes nicely and gets awesome mpg's.

Tell your teacher to go back to school... or at least give you ALL the facts instead of the ones that are slanted in favor of his opinion.

Mike

[240sxfan6882]

I had the Injen CAI with the "extension" that places the cone right behind the bumper. I remember paying quite a bit for both.
The power increase, if any, was next to nothing. It DID make my car more sluggish at low speed though, but at mid to higher RPMs it sounded cool because of the aluminium piping not dampening the suction sound.

I then blew money and got a Hotshot header and a 2.5" exhaust all the way, and again, all I heard was a louder car and really no HP boost.

I thought it was a waste of $$$$ trying to make the KA breath better, and it doesn't seem to respond to basic bolt on mods very well either.

I just went turbo KA, and of course, that was a whole other level lol.

I wouldn't do it again for any other car that I owned, unless it was turbo and those are easier to get power out of.

[Hashiriya415]

All new cars already have cold air intakes. What is there to improve on? Just because the pipe you bought is bigger doesn't mean it's needed. If you think a bigger pipe will give you more power, there is so much space in the engine bay you can fit 4 pipes. 4 filters.
Removing factory intake is retarded, all your doing is putting a filter in the engine bay to suck up hot air which is worse then factory.
Also running that new metal pipe versus the factory plastic will get heated from the radiator transferring heat to the metal pipe. Factory plastic stays cold.

[pacotaco345]

Whenever I ran a cold air intake on my stock ka it was because I picked it up for $20 and it looked cool. I had pretty much every "bolt on" that people do to those motors (intake, exhaust, header, emissions delete etc) and while the motor was healthy and strong I can't say it worked any better than a stock one. Also, the stock intake gets its air from outside so it is cold air. A "cold air" intake just relocates the filter to inside the engine bay and replaces all the bendy piping. You're actually sucking in warmer air due to the engine bay temps.

[Mikester]

^^Not true^^

There is a difference between a CAI and a short ram. CAI physically relocates the filter element out of the bay and into the airstream. A short ram replaces factory plastic/rubber with metal but keeps the element in the bay...

Also, colder and better are not necessarily synonymous when it comes to the temperature of intake air.

[pacotaco345]

^^Not true^^

There is a difference between a CAI and a short ram. CAI physically relocates the filter element out of the bay and into the airstream. A short ram replaces factory plastic/rubber with metal but keeps the element in the bay...

Also, colder and better are not necessarily synonymous when it comes to the temperature of intake air.

Mikester, I acknowledge your point and it is true. There's a reason why I put "cold air" in quotes. 99% of people who own a 240 will put a short ram or tube intake in their stock car and mistakenly call it a cold air intake. Which is what I think OP is doing. Also regarding the colder isn't always better comment, I'm sure there may be a certain hypothetical situation where its not better.. but there's a reason why "turbo weather" is associated with cold weather.

[DJ 21o3]

Long story short, mods do very little but add up as you do more. In the end, you need a proper tune to actually benefit from even the smallest mods.

If you want to really blow your mind, do some research on "hot air intakes". lol Not for performance, but for gas mileage..

[AdamR]

coming to this place for this sort of advice after you just heard from an actual teacher in a school... :barf:


He is trying to steer you in the right direction, without giving you the nitty gritty details that would take five hundred hours of reading by yourself in a dark room.

To lightly glaze the subject, since I have 6 minutes,
1. your exhaust system should be as small diameter as possible to maintain exhaust gas velocity, while also being large enough to permit the highest flow-rate requirement of the engine at peak horsepower without allowing pressure to rise in such a way that it impedes the flow of the intake event.
The factory exhaust of the 240sx is adequate for up to about 280 Horsepower at sea level, and should not be changing by anyone using a naturally aspirated 4-cylinder such as the KA24DE or even an sr20det with a stock turbo for any reason.

2. The factory air box is designed to protect the engine, where, so called cold air intakes not so much. The paper filter is the best filter you can possibly use to protect the engine. K&N Style, and others, do filter well, many of them- but not quite as well as the factory style paper gaskets do. They are more restrictive when they get dirty, and like the exhaust example, impede the intake event as they become more filthy. "Cold Air Intake"- that term, on the other hand, can hold some meaning if it actually functions to bring in denser air from the outside, however, many engines are designed to operate with a fairly consistent temperature. For ex., when the factory tunes an engine, they know the vehicle will be in many different types of climates, it could be cold or hot outside. By making sure the air entering the engine has reached a certain temperature, they can more tightly control the conditions of combustion. If suddenly the temperature were to change, the fuel or timing maps will no longer be optimal.


So everything you instructor dude said is completely true.

I would have assumed you would be gone by now, but I guess most people have you blocked so you are just talking in your own echo chamber.
The info he got was bad. Cold air intakes do work, but the gains are small.
Saying an exhaust is good for up to 280 HP doesn't mean there aren't significant gains to be had by changing it. The stock SR downpipe alone is restrictive enough to be a significant HP gain when swapped for a good one.
By the way, all that stuff about temp changes is nullified by the MAFS