A cold air intake is popular among car modifiers and boy racers. They’re the ultimate picture of Fast and Furious-esque speed and power.
And, let’s be honest, they do look great! You’ll get them in a variety of colors (including plain black). The vibrant reds, greens, and blues make an engine stand out against the crowd.
But how practical are they? Does a cold air intake really add horsepower, or is it just for show?
This guide will explain what cold air intakes are and how they work. You’ll then see why adding a cold air intake (without modifying anything else) has very little impact on horsepower.
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What Is A Cold Air Intake?
A cold air intake is a specially designed automotive air intake. They’re designed to pull colder air into the engine than the standard part.
All cars come with a stock air intake. It’s how the engine breathes, sucking in oxygen to burn the gas or diesel.
In most cars, an air intake is little more than a plastic tube with a filter (air filter). This then feeds into the intake manifold, where it’s divided up (avoiding technical terms) into the various cylinders.
A cold air intake replaces the plastic intake tubing and filter. In the vast majority of cases, the intake manifold remains as stock.
Cold air intakes also usually come with a washable air filter, distinctly conically shaped. These allow more air past than the standard disposable paper filters in the air box. You also don’t have to throw them away!
At the same time, you’ll notice that the engine noise changes. It’ll sound throatier and more aggressive. Of course, the exact notes depend on the design and your motor.
Before you install a cold air intake, you should check if it’s legal. Laws vary from state to state. Unfortunately, they’re now illegal in most parts of the country.
You could still install one on a non-road car, such as a racing track car.
What Does A Cold Air Intake Do?
A cold air intake aims to bring cool air into the engine.
Each part is designed individually for a specific car. The intake draws oxygen from a location that’s naturally cooler than elsewhere.
It then uses a unique airflow design to maximize the rate of oxygen going into the cylinders. This (theoretically) increases the engine’s horsepower output.
Some performance cars come with cold air intakes as standard. However, almost all you’ll see are bolt-on aftermarket parts. They’re usually relatively simple to install, although you should get a mechanic to help if you’re unsure.
Does A Cold Air Intake Increase Horsepower?
The simple answer is yes – in theory. But if all you do is switch out the stock intake for a cold air model, it’ll have minimal impact.
Cold air intakes improve the rate at which oxygen gets into the combustion chambers. More oxygen means more powerful combustion when the spark plug fires.
This drives the piston down, cranking the crankshaft with more force. The flywheel and transmission then send this power to the wheels.
How much they improve this rate varies from model to model and car to car. On some vehicles, cold air intakes will have little-to-no effect whatsoever.
If you read the product descriptions and mission statements on aftermarket cold air intake company websites, you might be led to believe that these are miracle products that vastly boost your power output.
While it’s true that they can, you aren’t going to be flying into hyperspace anytime soon. Most offer almost negligible benefits.
That said, a cold air intake can be used alongside other modifications to produce a significant overall hp increase.
Why Does A Cold Air Intake Increase HP?
As mentioned, you won’t actually see much (if any) increase in hp from a cold air intake. But you will most likely find one or two extra horses (no matter how little of a difference that makes).
Here’s where they come from.
The physics behind cold air intakes is very simple. Cold substances are denser than hot ones.
As a simple example, consider water. It’s pretty clear that ice (cold), a solid substance, is denser than steam (hot), a gas.
(If you’re interested in the science bit, scroll down a few sections to learn more.)
Air contains about 21% oxygen at all times. Because cold air is more dense, there is more of it in a given space. This, therefore, means there is also more O2.
As you’ll remember from school, fire requires three things. The Fire Triangle comprises heat, fuel, and – wait for it – oxygen. In cars, the heat (ignition) comes from the spark, while the fuel is, of course, gas or diesel.
More oxygen means fuel combusts with more intensity. For instance, using bellows on a wood fire increases flame height and heat output. In reality, you’re increasing the oxygen flow – the same principle as a cold air intake.
How Much Horsepower Does A Cold Air Intake Add?
Again, such a generic question can’t be answered with a simple figure. It’s simply untrue to say that cold air intakes always add 10 hp or 5% of your engine’s output.
It’s entirely dependent on the following factors (and more):
- The design of the cold air intake
- The car’s engine design
- How cool the air coming through the cold air intake is
- The quality and cleanliness of the filter
- How well it was installed
Most companies will claim around a 5% increase in horsepower. Again, this depends entirely on your vehicle and cold air intake model.
Nevertheless, 3% to 5% is probably a realistic figure. If, by some miracle, you find that you gain even more hp, it’s a bonus.
To put some figures to that, your 200-hp motor might kick out 210 hp with a cold air intake. That’s a 10-horsepower gain – not too impressive, right?
(Of course, you could equally argue that 10 horsepower is still 10 more horsepower. How worth it is that to you?)
As you might expect, cold air intakes have a more significant effect on larger, more powerful engines. The bigger the motor is in the first place, the more horsepower a cold air intake will add.
As such, they’re worth considering for performance cars such as a Ford Mustang or a Dodge Charger. However, to be realistic, putting one on your falling-apart Honda Civic daily runner is hardly worth the bother.
Modifications To Add Horsepower Alongside A Cold Air Intake
The most effective way to add a cold air intake is to do other modifications alongside it.
Before you start modifying your car, remember:
- Car modifications might void your warranty (if applicable).
- You should declare all modifications to your car insurance.
- Most car mods don’t do much for your performance. The vehicle is still limited by road laws, manufacturer restrictions, and limitations from the laws of physics.
If you do decide to modify your car, remember to upgrade the tires and brakes, in particular. If you find extra power from somewhere, your car must be able to handle it.
Failing to do this is likely to result in a crash.
Here are a few suggestions.
This is always glanced over and ignored by many wannabe mechanics. But it’s actually the most effective way to “gain” engine power.
Through the lifespan of an engine, it gradually loses power. This comes from carbon buildup, rust, debris, and pressure loss.
In fact, once a car reaches 100,000 miles, it will probably have lost 10% to 30% of its original power output.
An engine rebuild involves stripping your motor down to its base components. These can then be cleaned or replaced as appropriate. New seals and gaskets repressurize everything.
After this, it’s put back together and dropped back into your car.
You could add a cold air intake at this point.
The rebuild is really just basic maintenance. You don’t need to declare anything about the rebuild on any legal forms since it’s still exactly the same. (You might need to mention the new air intake.)
However, you’ll almost certainly notice a massive horsepower increase – more than anything else can give you (percentage-wise).
After an engine rebuild, a remap is the next best thing to increase your car’s horsepower. Do it alongside a cold air intake to increase the effectiveness.
This can completely alter your car’s power output. You could make it focus on more power or more fuel economy if you prefer.
Take your car to an experienced remap technician. They can adjust the software in your ECU to utilize the increased airflow to the max.
You could choose to have them install a pre-coded chip, too. They’ll run you through your best options.
A vital thing to remember: don’t overdo it. It’s tempting to go for Stage 2 or 3 chips (with their corresponding mods). You’ll achieve nothing more than blowing your engine up if you aren’t careful.
Be realistic. If a remap or chip can offer you a 10% horsepower gain on top of the cold air intake, take it.
Again, you’ll have to declare this modification on your insurance.
It’s one thing to get more oxygen into the engine, but it’s almost worthless if you can’t then get the residue gases out. These essentially choke the incoming air, minimizing its impact.
By replacing your stock exhaust with a performance model, the overall engine airflow – from the intake to the exhaust tip – improves.
Again, a performance exhaust is unlikely to have any kind of huge impact on your horsepower. However, it and the cold air intake will complement each other, with a much better flow from start to finish.
If you can, it’s worth buying a cold air intake and performance exhaust from the same company. This way, you have the best chance of performance increases.
Legally, you may have to declare your performance exhaust on your insurance.
Even if you don’t see any hp gain with the cold air intake and performance exhaust, your car will sound fantastic. If anything, be careful it isn’t too loud – you don’t want to receive a noise complaint or get pulled over by the cops.
Forced Induction (Supercharger Or Turbocharger)
Before installing a forced induction system, you should carefully plan it out. Forcing too much high-pressure air into your motor could overload it and blow all the seals and piston rings.
It must be properly installed by a trusted mechanic. There are many challenging things to consider, such as new oil lines and quantities.
Superchargers and turbochargers both draw extra air in. Superchargers are belt-driven, while a turbocharger turbine is driven by exhaust gases.
You’ll see significant horsepower gains with forced induction. Pairing it with a cold air intake will provide even more oxygen (but hardly any in comparison).
Make sure you reinforce the engine and drivetrain before running a forced-induction kit.
Again, you’ll need to check all the legal aspects first too.
Why Is Cold Air More Dense? (The Sciencey Bit)
Here’s the technical bit if you’re interested.
What Is Density?
Density is (in physics terms) “the quantity of mass per unit volume”.
For example, a box filled with bricks weighs more (or, technically, “has a larger mass”) than the same box filled with feathers.
This is because the bricks are more dense; they have more mass occupying that space.
The Physics Of Hot And Cold
Temperature is just a measure of kinetic energy.
The more energy particles in a substance have, the more they fly around, knocking into each other and occupying as much space as possible.
A warmer material has more kinetic energy than a colder material. The cooler something is, the less “excited” its particles are.
Convection is related to density and temperature. It’s the rule that hot air (or any substance) rises, while cool air sinks. It’s almost always hotter upstairs than downstairs, for example.
Let’s go back to density for a moment.
Density can also be explained by thinking about whether something floats. If it does (for example, a cork or a whole ship), it’s less dense than water. If it sinks (like the aforementioned bricks), it’s more dense.
What Does This Mean For Cold Air Intakes And Horsepower?
Take these principles and apply them to air.
Hot air is less dense because its particles have more energy. They’re flying about all over the place.
Cold air is denser because its particles aren’t as active. They’re occupying a smaller volumetric space than the hot air.
Your engine will still suck in the same volume of air (using pressure differences). However, cold air weighs more than the equivalent volume of hot air – there is literally more of it.
In turn, this means more oxygen. And that, as explained above, means more power from the ignition and, thus, more horsepower.
Cold Air Intake Positioning And Density
One final note on density and cold air intake positioning.
You’ll usually notice that cold air intakes point or even bend downwards. This is typically different from the stock intake, which generally juts out horizontally behind the grille.
Why does the cold air intake point down? Well, refer to the above.
Denser things sink. Cold substances are more dense. Cold air falls while hot air rises.
This is where the cold air intake finds its colder air: simply by pointing downward.
Is A Cold Air Intake Worth Getting For More Horsepower?
So, you want more horsepower? There are better options than a cold air intake.
In the end, a cold air intake for a road car will do very little other than change the engine noise. You’ll see tiny horsepower increases. They’re more for show than anything in most cases.
With that being said, you could use it as part of a series of modifications. Expect minor horsepower gains from these individually, but you might get more significant results when they’re combined.
Then again, if you just want your car to look as cool as possible, a cold air intake is a great place to start.
If you’re thinking of installing one, K&N is the most reputable brand on the market. They’re good value, too.
Get it installed by a car mechanic if you’re unsure what you’re doing! And remember to check the legal requirements!