OEM Large Airbox

[Adz The Heeb]

Hi All!

Why do most normal road cars come with a large square airbox and panel filter with lots of plastic?

Why do you rarely see cars come with a simple conical air filter?

Is it purely to reduce intake noise? Or is it to increase the surface area of the filter?

They seem over-engineered. They also usually sit nicely above the cylinder head where they seem to just act as an insulator stopping the heat from escaping.

I'd be very grateful if someone could explain the reasoning behind this.

Thanks,

Adam

[edited to make more sense]

Edited by Adz The Heeb on Wednesday 19th February 19:42

[john banks]

Ducting of cool air, noise reduction and correct airflow pattern presented to the mass airflow sensor(s).

[Another Fluffer]

A conical filter is more open to the elements, therefore would have to be replaced more often - increasing cost etc.

[Adz The Heeb]

Thanks, those points make good sense.

On my Punto for example, the air box is massive, but the ducting leading up to it is only small in diameter. Maybe it's for the MAF sensor as you say.

[anonymous-user]

Because, contrary to what most "modifiers" think, that design is the best way of ensuing the minimum intake restriction, best filtering performance, low intake noise (too meet driveby regs), suitable intake tuning (frequency response to suit car market), optimum dynamic pressure recovery at speed (pressure ram), Low upheat of incoming charge air etc.

But of course, the people who sell you a simple open "performance" cone filter know all about that stuff don't they...........

[ToothbrushMan]

Dont think the conicals help hot starts because of heat soak.they may not pass regulations in respect of noise too.

[lemonslap]

Another Fluffer said:

A conical filter is more open to the elements, therefore would have to be replaced more often - increasing cost etc.

My 2010 Audi S4 has a conical air filter as standard and it's change interval is 57,000 miles

[Adz The Heeb]

Max_Torque said:

Because, contrary to what most "modifiers" think, that design is the best way of ensuing the minimum intake restriction, best filtering performance, low intake noise (too meet driveby regs), suitable intake tuning (frequency response to suit car market), optimum dynamic pressure recovery at speed (pressure ram) , Low upheat of incoming charge air etc.

But of course, the people who sell you a simple open "performance" cone filter know all about that stuff don't they...........

Very interesting. I don't understand what you mean by 'frequency response to suit car market'?

And when you say dynamic pressure recovery, do you mean that the large airbox acts to slow the air down at high speeds and create a sort of storage tank?

Thanks for the responses.

[anonymous-user]

Everything about a modern car is tuned. The intake system is modelled in detail, using computer simulation, and in conjunction with an acoustic model of the cabin, the exact "note" (ie frequency spectrum) of the intake noise, both in the cabin (to suit market, ie sporty cars - gruff and loud, prestige cars, soft but bassy etc) and external (to meet drive-by noise limits). The exact size of the airbox, and all the pipes and even resonators(closed ended) is to make the car sound like the OEM wants it too.

By using a high volume airbox, the intake air is slowed right down, which increases the air pressure (good for performance) but also creates an even flow through the full area of the filter element, so the pressure losses are minimised

[JonnyVTEC]

OEMs like keeping engine oil use down whilst on warrenty so they fit stuff that does a good job filtering the air!

[10 Pence Short]

When I had my EP3 people used to laugh at the Mugen airbox for being just a big glass fibre box with a large flat filter (the oem was a small chambered affair with a conical filter).

It obviously wasn't bling enough for many, but by god it did the job.

[Another Fluffer]

lemonslap said:

My 2010 Audi S4 has a conical air filter as standard and it's change interval is 57,000 miles

Fair enough, however I assume it is contained in an Airbox as opposed to being completely bare in the engine bay

[supersingle]

Max_Torque said:

Because, contrary to what most "modifiers" think, that design is the best way of ensuing the minimum intake restriction, best filtering performance, low intake noise (too meet driveby regs), suitable intake tuning (frequency response to suit car market), optimum dynamic pressure recovery at speed (pressure ram), Low upheat of incoming charge air etc.

But of course, the people who sell you a simple open "performance" cone filter know all about that stuff don't they...........

It's not that simple is it? Tradeoffs have to be made. The tradeoffs an OEM will make might not be the same as those made by a car enthusiast. For instance an OEM is likely to chose inlet runner lengths to suit midrange power whereas an trackday driver may favour more top end and a screaming intake noise to boot!