Open vs Closed Box Intake - Which is Better?

Nowadays, one of the most common modifications enthusiasts make to their cars is adding performance intakes. Not only do they make the engine bay look much better, but they also add horsepower and torque and sound incredible. Intakes are designed and sold with or without an airbox, giving rise to one of the biggest debates within the performance intake industry: Which is better, closed or open box intakes? While both of them have their pros and cons, we generally suggest an open box design for the turbo-diesel platforms. Read on to find out why.  

What is a performance intake?

First off, let’s cover exactly what a performance intake is. They are usually a replacement for the factory intake system. Performance intakes use a new design that typically includes larger diameter and less restrictive intake piping, combined with a larger filter that is usually cone-shaped. Sometimes, they come with an airbox that encloses the cone filter, but not always. These are in contrast to the stock units, which are usually much more restrictive in their tubing, airbox, and filter design.

The larger diameter of the performance intake tubing and cone filter compared with the stock units allow them to suck in more air, which lets them make more power. In addition, the less restrictive tubing also pushes the air to travel faster and easier, again equating to more power. Most intake kits use either K&N or S&B filters, which are the top two choices on the market by far. They offer excellent reliability and performance without breaking the bank.

For many people, a performance air intake is the first mod they do to a car. Usually, they are good for about 5–15 wheel horsepower and torque with a tune. 

Ram Air vs Cold Air Intakes

There are two different types of performance intakes, ram air and cold air intakes. Both of them have their pros and cons, but they are relatively similar. The difference between them is the placement of the air filter. On turbo–diesel short ram intakes, the air filter is located as close to the turbocharger as possible. This ensures the shortest possible path from filter to engine, meaning the least amount of restriction.

In contrast, cold air intakes relocate the filter outside of the engine bay, usually toward the fender area. This allows cold air intakes to take in the coldest air possible – hence the name. In theory, cold air intakes should make more horsepower because they take in colder air than normal. Colder air is more dense and has more oxygen, meaning it is better for making horsepower.

However – and this especially true on a turbo-diesel – the air is already going to be heated up as soon as it enters the turbocharger and becomes compressed. In addition, most turbo-diesel systems use intercoolers, which are very effective at reducing charge air temperatures. Both of these combine to make the difference between a short-ram and a cold air intake pretty miniscule in most cases. 

What is an airbox?

Airboxes are used on cold air intakes as a way to mitigate heat soak. They are small enclosures that cover the air filter to separate it from the surrounding engine bay. The idea is that they will not only shield the filter from the heat of the engine and turbocharger(s), but also from the dirt and debris that is loose in the engine bay. Next, we’ll go over the pros and cons of both closed and open airbox intakes.

Benefits of Open Box Intakes

There are a few benefits of open box intakes, the most significant of which is probably the price. Airboxes, though you might not think so, can actually get pretty expensive. On some models, they can add as much as $100 over an open box version. Saving $100 on an airbox lets you buy other parts that could potentially add more horsepower. 

Another pro of having an open box intake is that they tend to flow a little bit better. While the airboxes do have a small opening in them or are bottomless/topless to allow in air, there is definitely some restriction. Some airboxes are smaller than others, and they can actually choke the amount of air getting to the filter. Having an open box filter completely mitigates any of these concerns or problems, and allows for the best possible airflow. 

Open box intakes are also more often louder than closed box versions. The reason is pretty obvious, as the box muffles the sound, so removing it will make it much louder. Most people like to hear the sound of their aftermarket parts, and you can usually hear the turbo and blow-off valves a little bit better, too. 

Finally, an open box intake is much easier to install than a closed box intake. Airboxes have also been known to rub on other parts and cause premature wear. Which can create a whole new set of issues from nothing. 

Benefits of Closed Box Intakes

While there are supporters of open box intakes, there are also many people who prefer closed box intakes, too. While they are more expensive and harder to install, for some they are the preferred choice. One of the biggest advantages of a closed box intake is the reduction in intake temperatures. The airboxes cut off the filter and insulate it from the engine heat, which means colder, denser, and more oxygen rich air.

In addition, airboxes also keep the filter cleaner than an open box design. The airbox shields the filter from unwanted dirt and debris, potentially prolonging its life and making it perform for longer. Depending on the setup, airboxes can also help reduce air turbulence on mass airflow (MAF) based systems, resulting in more precise readings and fueling. 

Closed Box vs Open Box Intakes: Which is Better?

While both closed and open box intakes are good, we generally recommend going with an open box design. Not only are they priced much better and more affordably, but they perform just as well if not better than those with airboxes. They both perform the same, and the open box intakes sometimes outflow the closed box intakes if the airbox is a restriction. 

The one edge that the airbox really has for it is a reduction in intake temperatures, but on a turbo-diesel that is largely mitigated. To start with, the air seriously heats up the second it enters the turbo and becomes compressed. This means the 10-15° difference in temperatures is pretty much meaningless as soon as it’s sucked in.

Additionally, most turbo-diesels are equipped with intercoolers. These are designed to reduce charge air temperatures as much as possible, and should have no trouble adequately cooling open box units. If you are really concerned with boost temperature, you’re better off taking your savings from an airbox and putting them towards a larger intercooler.

FAQ

What is a performance intake?

A performance intake is an aftermarket intake that increases horsepower and torque over the stock unit. It does so by adding bigger and less restrictive tubing, and a larger cone filter. 

What is the difference between Ram air and Cold air intakes?

Ram air intakes and cold air intakes are very similar, with the difference being filter placement. Ram air intakes place the filter as close to the turbocharger (on a turbo-diesel) as possible. This allows for the least restriction possible. In contrast, cold air intakes relocate the filter away from the engine bay, usually by or in the fender. This allows for cooler and denser air vs a ram air intake – though the difference is not very big on a turbo-diesel.

What is a closed box intake and what are the benefits?

Closed box intakes are cold air intakes that utilize an airbox. Airboxes are enclosures that surround the air filter. They cut them off from the heat, debris, and dirt, flying around in the engine bay. Many people prefer them because they can allow for lower intake temperatures and keep the filter cleaner. 

What are the benefits of an open box intake?

Open box intakes are usually cheaper than their boxed counterparts. They also flow better because there is no restriction from the surrounding airbox. In addition, they are easier to install and sound louder and better than closed box intakes.

Closed vs Open Box Intakes: Which is Better?

Generally, we recommend and prefer open box vs closed box intakes. Open box intakes are cheaper, flow a little bit better, are easier to install, and sound better than closed box intakes. Especially on a turbo-diesel system equipped with an intercooler, most of the benefit from an airbox is lost before the air reaches the engine anyways. Closed box intakes still perform adequately, but they are generally more expensive.