Tuning guide "Induction kits & cone filters"

Like all of us, car engines need to breathe. They use an air fuel mixture which has to be precisely balanced into what is referred to as an air to fuel ratio or AFR.

For petrol engines 14.5:1 is the petrol cruising AFR but under load the engine needs more fuel, with typically around a 13:1 AFR. In a turbo engine the AFR might be 11 - 11.6:1.

A lambda sensor sniffs the exhaust and determines the amount of unburnt oxygen and will adjust the fuelling to maintain a clean efficient burn avoiding running rich or lean.

The prime motivation for fitting an induction kit is generally to get the lovely induction roar sound that is muffled by the air box. In larger engines, high performance engines and turbo engines you may also see slight top end power gains.

Adding an induction kit allows a car to suck in air more freely. Induction kits typically comprises a cone or hemispherical filter with no air box. The idea is that more air can enter the engine. The standard paper filters that car have in their air boxes are somewhat restrictive to airflow.

A performance air filter needs to compromise between filtration and drag. They are generally made from foam, gauze, cotton or a mixture of the three. We have found that cotton filters give the best filtration to reduced drag.

Oil is generally used to aid the filtration as it traps the small particles of dirt instead of allowing them to flow into the engine. We read much online of problems caused to AFM/MAF (intake sensors) caused by oil fouling. In reality this will only generally happen if you have primed the filter with too much oil so there is little to worry about as long as the filter is properly maintained.

Induction kits should not be confused with performance air filters. The latter fit in the OEM intake box and are swap in replacements. An induction kit replaces the air box and is generally a cone, cylinder or hemisphere shape. Good induction kits include a cold air feed, some type of partial air box to shield it from engine temperatures and full fitting instructions.

One advantage of induction kits is the fact that most are washable and will last for many years, saving you from buying a new paper filter each year. (Although considering the low cost of paper filters it doesn't make economic sense to buy an induction kit if you just want to save money in the long term.)

You certainly get what you pay for and cheap one size fits all induction kits do little for performance or sound.

If the engine can suck in more air then it is able to burn more fuel so you are effectively increasing the efficiency and power output of the engine.

"Not all engines will benefit from an induction kit!" 

It is worth noting that not all engines will experience power gains from an induction kit. Smaller engined cars (those under 1.4 especially) will actually feel less powerful with an induction kit. In this case you should use a panel air filter which replaces the standard paper one inside the OEM air box.

Bear in mind that a standard air filter has a much greater surface area than the intake pipe and this generally makes up for the drag caused by the filter.

Some manufacturers use the same airbox across a range of cars and where this is done the more powerful engines are effectively restricted.

In smaller engines a certain amount of excess oxygen will not be matched with fuel as the injectors are not big enough and cannot keep up. This causes the engine to run lean. An air filter should also be matched to a good exhaust system to allow a balanced flow through the engine. More air in means more exhaust gases.

In all cars, induction kits will suffer from a higher intake temp due to the hot under  bonnet temperatures unless they are sited inside an air box. We all know that hot air carries less oxygen.

Removing the air box makes the intake temperature rise as air is taken from this hot region rather than from a vent taken from a cooler place.

You can negate this issue by adding a cold air feed pipe which pulls in air from outside the engine bay. Some manufactures take air from the front wing or just behind the headlights but there is nothing stopping you from cutting a new vent in the hood to allow in fresh cold air.

Most dyno runs are taken with the bonnet open so will not reflect real world power gains. To combat this problem add a cold air feed to pipe in fresh cold air from outside the engine bay.

This entry was posted under air intake, engine. Tags: filters, induction kits
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