I am interested in cars and do my own repairs where I can. I like to share any knowledge I have to help other people where possible.
Brum Brum. Squeeeal. Waheeeey!
At some point when owning a performance car, or if you're young, a slow car that you'd like to squeeze more performance from, the question comes up. How can I get more power out of this thing? How can I burn people off at the lights and generally feel like more of a boss, while attracting the attention of beautiful women?
Well, one of the ways that you can do this (at least this is what the marketing people tell you) is to fit a performance air filter or a full induction kit—a K&N or Pipercross, or something that looks like that but is unbranded, which you can get on eBay. Hey, you can always put a K&N badge on the back of your car and get the respect of the rest of the barry boy racers, so it's all good.
What's the difference between an induction kit and an air filter?
An induction kit usually comes with pipework, the idea being that you'll have the filter, which is usually cone shaped, situated somewhere it can suck in cold air, usually at the front of the bumper or somewhere else close to air flow. A filter without the induction kit is usually just put in place of the airbox and sits in the engine bay. Or there is the other type, the drop in filter, which is made of foam/gauze and sits in the air box, in the place of the standard paper version.
Do performance air filters actually work?
So, do these performance air filters work? The marketing bumph tells you that they will. I remember when I was a young man with a low-powered car and my friend told me that his friend had told him that you could get an extra 40bhp out of your engine with performance spark plugs and a K&N filter. Obviously, I soiled myself on the spot; that would have meant 50% more performance from my measly engine for practically no money. What a bargain. So I got the plugs and filter.
The car was a lot noisier. Was it faster though?
How do they work? What is an engine?
These filters work on a fairly simple principle. Engine power is created from fuel and air being mixed. If you put more of both in, then you'll get more powwwwwwwwwer. So the idea is, get a filter that doesn't restrict the air flow (or is at least less restrictive). The engine will then suck in air easier, the engine management system will provide more fuel and then the power will follow. Yeehah!
So, what's the problem? Is there one?
After driving cars with and without performance filters and noticing that the ones with the performance filters were louder, I thought I'd do some reading. These filters do let a bit more air through. A bit, anyway; in an independent real-world test, the top performing air filter on the market, the K&N filter let through 0.14% more air than a standard paper filter.
From a performance perspective, this isn't great. But the airflow into the engine is only part of the story with an induction kit. The noise from the engine is definitely increased and that is pretty good for most people that want to actually hear something going on when they press the loud pedal!
Hot air? Cold air? What's the difference?
The downside is that a lot of these filters come in a cone shape and require you to remove the factory air box. Because of this, they then suck air in directly from the engine bay, which is hot. As you will no doubt remember from your physics lessons, air expands as it heats up, which means hot air contains less oxygen than cold air.
Less oxygen is not what you want from your air, as this means that the air is less combustible. Cold, high-oxygen air is what your engine craves and is the reason that turbocharged engines use intercoolers; you need to get that air cold before your engine gulps it down if you want to extract maximum power from it.
If you have an unshielded cone filter, then you will only be getting good cold air flow to the filter when you are going very fast, so there is a lot of air flowing into the engine. It's not practical to be driving at 100mph+ just to get cold air flow . . . most of the time, anyway.
What this can mean is that until the air is flowing into your engine quickly enough to negate the heat soak from the engine, then you'll actually lose performance with a performance air filter. This will happen at low speeds and especially from a standing start. If you've been idling at traffic lights for 20 seconds, the air under the bonnet is very warm. You pull away and your car is down on power until enough air has flowed in to replace the hot air. Not really what you want from a performance upgrade.
A drop-in type that replaces your paper air filter directly in the air box won't suffer from this problem, but a cone will. Pretty much the opposite effect you're looking for when you buy one of these is less power, but if it's unshielded, that's what you'll get.
They do make a louder noise though. Brum Brum!
If you want to do it properly then you'll need a fully shielded induction kit. These aren't going to be perfect at stopping heatflow, but are much better than an unshielded cone.
One of these will still sound good and you won't see a performance drop after idling.
Here's the conclusion.
Although there is a lot of good marketing bumph out there, a lot of it is just that. If it's outright performance you're after, your first step should not be a performance air filter/induction kit; instead, you should focus on either losing some weight from the car or getting a remap. Or both! With an induction kit, although it won't make you faster, you will get a louder/better noise as you can really hear the engine breathe, which is, of course, desirable for a lot of people.
My advice is just to keep your paper filter regularly changed and not worry about a high-flow filter. If you want to fit one for the noise and you're after performance then make sure you don't leave the cone air filter exposed and instead fit a fully shielded induction kit to ensure that the air that goes in is as cold as possible.
If you don't shield it, you will get more airflow at high speed, but off the line, it can actually be a bit slower down to heat soak, the engine heating up the air under the bonnet, which is then sucked in by the filter when you start moving. That is not cleared until you've been driving for a few seconds, so initially, your car will actually make a bit less power if your intake is not shielded correctly. You don't want this!
Remapping is definitely a solution that will get you more power than just replacing the air filter for an induction kit. That is something for another article though.
Thanks for reading. Please leave any comments below.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
© 2012 Rain Defence
Tom on June 27, 2020:
Depends on your goal. (2002 GMC Denali, Vortec 6000, original 302 HP, well maintained. 185K miles. All time 4 wheel drive. All comparisons after tune-up.
1. Real horsepower improvement: not a whole lot ( Engine HP at this age, after tune-up approx 240 HP. 5 - 10 HP improvement on dyno 2% to 4% improvement. Done with regular gas.), unless you never changed your old air filter.
2. Idle RPM dropped from 650 - 750 to ~ 500, on tach.
2.A. Real problem, AC compressor does not kick in until engine RPM is greater than 550 RPM. In hot weather, with AC on, long stop light, can sense AC cooling loss. Comes right back on with stepping on gas to either rev engine or accelerate from stop.
2B. Real advantage: Recognize ~ 5000 pounds vehicle. Gas mileage improves from 12.3 to approx 12.8 mpg with my mixed driving, repeatable. Actually allows K&N square filter element to pay for itself. It would take a lot of driving to offset the cost of the conical filters.
2C. Repeatable to watch mileage and RPM changes go back to pre-K&N filter as filter element gets dirty. Clean filter and the improvements return. And appropriate tune-up.
This one took a while to understand: Pre K&N filter: 70 MPH at 2200 RPM. Post-K&N filter: 70 MPH at slightly less than 2000 RPM.
Drive train is same, represents effect of lower idle RPM. Minimal less stress on engine and better gas mileage. RPM for speed depends on RPM for that speed ( from Drive train set up + Idle speed RPM ).
This is more noticeable than actual possible HP increase in this vehicle.
So all in all, kind of fun. Minimal better HP, probably not noticeable, but money saved more than offsets cost of filter.
Busa James on August 20, 2019:
I love k&n filters i use them on my turbo hayabusa, and believe me when i tell you on a properly tuned and built machine theres a difference. You get what you pay for. so spend a couple dollars and get a couple ,spend alot and get alot simple sience
Johnny gNOS on June 06, 2019:
Thanks for the advice. Putting the stock box back on now. I hate the heat, so i imagine my car does too. ✌️
TomTerrific on April 14, 2019:
Everybody can put anything they want on the internet and sell ice to eskimos. For every article that says performance filters don't work, there are two that will say they do! But for these two that say they do, there might be three more that say certain ones are actually ruining your motor and destroying your ride. And they have scientific terms that make sense in their articles. I would say the bottom line is if you put a $50 air filter in your vehicle and feel like it is going faster, go for it! These people (K&N) have been in business for many many years, even buy this author's account, and are still slinging those air filters for $50. I would say if their product was truly debunked, it would not still be on the shelf of every autopart store in America!
But hey, I put one on my ford ranger in 2006 and never felt a noticeable difference. But I wasn't keeping a scientific log either. Just trying to get to work faster, using less gas, like everyone else, right?
I would say if that was your goal (to get there faster, using a little less gas) they work just fine. But common sense says don't expect a $50 air filter to turn your ford ranger into a race car.
Go get a supercharger and open up your exhaust, then tune it!
Tee Sherbet on January 12, 2019:
Hi. I run a company called Comkotes and I think everything in this article is rubbish. Hot air = more bhp! Feed it hot!
Boom on December 10, 2018:
now all you fools that think your fast and furious - take that fart can and hot air intake off your car. You don't know what you are doing. But - doesn't matter. Even with science they are too dumb to do the right thing.
scy128 on May 22, 2018:
We specialize in the production of filter . We can produce the OEM. www.china-futong.com
Jeremy on March 17, 2018:
Can I use another cars short ram intake on my car if the cars are different models
Nikhil on January 19, 2018:
Very informative honest review. Truly appreciated !
eddison cassius on October 12, 2017:
Nice word of speech bro. Fully overstand your definition
Vinny on August 31, 2017:
Brilliant article,,confirmed a lot of doubts I had,,it can't be that easy lol,cheers
Lu on November 05, 2016:
Many thanks to the author and KevSutton! You just saved me $300.00 and won't ruin a perfectly good running engine in my jeep!
Ron on July 12, 2016:
I fitted the Pipercross to my wife's MX5 as we've just added simple things that actually improve the car such as the mesh grill to protect the radiator from stones. She wasn't convinced there would be any difference but, she says it actually feels as if there is just a little bit more power. She also likes the sound. It's not louder but just has a nicer growl that makes it easier to hear the engine for gear changes. So, that's the view of someone who had no faith ...
Not Amused on June 01, 2016:
....... Okay this article while having some ground is mostly crap. A cold air intake will increase power and throttle response, most cars computers require a tune to use them so the MAF sensor isn't freaking out. If you're have problems with a cold air intake chances are you're doing something wrong or just bought a cheap one off of eBay. Performance has so many components, but at the end of the day an engine is gas, air, and spark. You up the ratios on one of those you can get more power, it just has to be controlled.
Snapper on March 04, 2016:
Panel filters are the way to go and if you duct feed cold air direct to the air box you will get a few extra bhp.
Piper cross foam filter allows a lot more air to pass but any non paper filter will be better than standard.
In reality, you will struggle to notice 3% power increase.
Chris from Tampa, FL on October 15, 2015:
some excellent points here. In most cases an intake will not make more power. That being said it can become necessary as other parts of the engine are modified. https://hubpages.com/autos/5-best-low-cost-modific...
Brandon on October 09, 2015:
Cone filters are dumb. Most cars already come with a nice CIA intake. The most you'll have to do to make it "perfect", is to tweak the pipe coming into the air box to match the size of the one leaving it, and add a drop in K&N/Spectre panel filter. You'll get a bit better throttle response, which does make it feel more a little more powerful to the driver when you gun it.
jjj on July 15, 2015:
Farhan on February 06, 2015:
This is certainly a good and informative article. Thanks.
P/S: To the user "Rahn Razamai"
You should've said that website is only for Malaysians. It killed my excitement when I saw it was in Malaysia only. *sigh*
Rahn Qarnain R Razamai from Rawang, Selangor on February 05, 2015:
nice article. visit http://ikutkiri.com/ for car parts at reasonable price and good quality.
Kevin Sutton from Gulf Shores, Alabama on November 11, 2014:
great article very informative been messing with cars for years but sometimes forgot this fact. But like the race cars saying doing drag races. what they do is run a pipe from engine to the front fender so the filter is located outside the car itself so it wouldn't be heatsoaked. But now it's exposed to more pollutants but pulling more air in the for combustion...it's like 70/30. not even 50/50. More harm would be done to the engine over time but it will give the race car driver a faster 1/4 miles which is the goal in race situation not really longevity. But for the everyday driver it's not necessarily the best option. And the gains are more seen with big horsepower applications like anything over 300 hp, then you have to replace the air filter of course. But that is not a standalone activity because the fuel system has to match up with the airflow if not your engine will be running lean too much air and no fuel to ignite the mixture. So yeah there is a few things to consider.....
Daniel on February 26, 2014:
Well authored and answers a LOT of questions yet I have questions concerning cone shaped filters as I have found some sort of assembly on Ebay called [ 3" REAL CARBON FIBER AIR STACK FILTER/INTAKE HEAD SHIELD FIT MOST CAR 2.75~3.25 ] of which can be searched w/o the brackets and sorry for the long string but happy hunting.
-hey- think MAF sensors are crashing due to thermal issues? Try running them in the desert. Are there any ideas of people using heatsinks, air compressors, Freon - Air Conditioners to cool the air on the intake or is that a stretch of the imagination (at this point)?
The item depicted actually comes with or HAS a FULL CANISTER SHIELD. But is it a shield? Your article really has me looking for shields now instead of merely drawing warmed air into my intake. Sounds like a mistake! Will such a 5'' can made of carbon fiber aid in this battle of the thermals? I'm looking at 'the green shroom' pic under 'cold air intakes' and that um, kinda helps with the problem, but dose not fully answer the question. Thanks much!
Afterthought: I'm not concerned with the noise, though, if I had a choice (of mufflers?) then I'd probably try to keep a low-erd profile as I am not in the running for announcing STEAL MY CAR to the 'world'. If you know what I mean, great. If not, thank god. I'm really more concerned with heat shielding than grunt noise :)
Rain Defence (author) from UK on January 08, 2014:
Have you had it on a dyno or does it just 'feel' faster? Either way as long as you're happy, then it's all good.
Carlo on January 06, 2014:
I run a K & N replacement filter not pod in my Turbo Mercedes and you definitely can notice a small gain in power and better response. Well worth $70.00, just need to keep it clean every 5,000-10,000kms.
Rain Defence (author) from UK on August 01, 2013:
I suspect the only reason they're often cone shaped is because of the way they look. A lot of manufacturers make them cylindrical as well. I can't see there being any real difference in flow between shapes, surface area is the only real factor with these.
I'm thinking of buying another v8 car soon and will probably get one just for the noise even if it doesn't make it faster!
John R Wilsdon from Superior, Arizona on July 31, 2013:
Thank you for the explanation about performance air filters. I have wondered about that, and you have satisfied my curiosity. Is the cone shape to start a venturi effect? I drive a 2.2 liter 4 cylinder truck. I love it because it is great on gas (for a pick up). Kinda pointless for me to buy a performance filter or induction kit just to hear a whistle like a jet! Everybody will still pass me when trying to pull a hill. But that's ok with me.
Onlinestrategies on May 18, 2013:
Thanks for explaining how the air filter works and why one should not change the factor fittings for obvious reasons.
honda-stream from Canada on May 07, 2013:
I love the sound of a good Air Intake! A nice little purr, the small performance increase is great too :)
Tom on April 06, 2013:
True I've seen cold air intakes cause more problems then gains such as heat soak from the exposed filter under the hood and metal pipping, check engine lights, and cars going into limp mode. But they do sound nice on the car. Lol
Magillacutty on March 16, 2013:
I have a K&N rx-3900 on a short ram, with a cold air feed and heat shielded. Compared to my restrictive low flow factory air box I believe that my car (2.0t, 194 kw [atw], 1100kg, 18psi) spools up quicker and is more responsive on throttle. Look each to their own but I won't go back to factory... Oh yeah the noise!!! =D madness. Cheers Mgt.
jocent on March 08, 2013:
You're right it only gives good sound and little power because of faster airflow. Cold air is the one that helps increase boost and economy. The only thing you can expect from performance filter is the one time replacement. Thanks for the tip!
Liheng from Shanghai on March 05, 2013:
Rain Defence (author) from UK on February 08, 2013:
Thanks for your comment
newusedcarssacram from Sacramento, CA, U.S.A on February 07, 2013:
Hi, thanks for all the information. It was a good read.
Rain Defence (author) from UK on January 18, 2013:
It's true. They sound good and I think that's the only real benefit. MAF sensors are very sensitive.
Shea on January 17, 2013:
These ram air filter kits actually cause more 'check engine' light problems than anything else. The mass air sensors don't like the change.
Rain Defence (author) from UK on November 16, 2012:
Oh yeah, they might not make it faster, but you're right, they do sound great, especially on turbo charged cars where you can really hear them!
chriscamaro from Ontario, Canada on November 16, 2012:
I've got a K&N panel filter in my ram air setup and it amplifies the "whistle" that I already had. I don't mind... I think it adds character :)
Scott Beyer from North Carolina on October 12, 2012:
They make a real mess of Subarus computers... can't get them to pass inspection with a reflash, and I still haven't seen any significant gain. May try one on my 71 beetle, might see 53hp!!! That's total, not gain.
Rain Defence (author) from UK on October 12, 2012:
Nothing like a loud air filter on a diesel. Really accentuates the noise..
dommcg on October 12, 2012:
those look awesome, I think I might get one for my Volvo!