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Do Performance Air Filters, Cold-Air Intakes and Induction Kits Work?

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.

Get ready to wheeeeeelspin!!

Get ready to wheeeeeelspin!!

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?

Before K&N

Before K&N

After K&N

After K&N

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.

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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.

You should hear it roar now I've fitted the induction kit.

You should hear it roar now I've fitted the induction kit.

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.

If you have the filter unshielded in the engine bay like this, it sounds great but won't give optimum performance.

If you have the filter unshielded in the engine bay like this, it sounds great but won't give optimum performance.

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

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