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Phazer
02-27-2004, 04:42 PM
Thinking of doing the fogged airbox mod, but just want to get some info, what's the differance between a fogged airbox and a CAI? Fogged airbox, bigger hole in it with wider pipe going into it, and a CAI is a cone filter behind a heatshield? Or am I totally wrong here?

Is a fogged airbox worth it on my 323i? Won't it screw up your airflow meter thus getting the wrong reading of the amount of air entering your engine and thus decrease preformance?

Autotechnica
02-27-2004, 08:10 PM
Originally posted by Phazer
Thinking of doing the fogged airbox mod, but just want to get some info, what's the differance between a fogged airbox and a CAI? Fogged airbox, bigger hole in it with wider pipe going into it, and a CAI is a cone filter behind a heatshield? Or am I totally wrong here?

Is a fogged airbox worth it on my 323i? Won't it screw up your airflow meter thus getting the wrong reading of the amount of air entering your engine and thus decrease preformance?

You're correct. CAI is usually a cone filter that is placed behind your bumper with piping that goes into your MAF. A fogged airbox is basically just using the stock airbox but with an extra pipe that goes from your bumper or front grill to the side of your stock airbox.

It won't mess up the MAF since it still decides how much air is being sucked in. You could put in a 100cm wide cone air filter and it wouldn't make any difference to the amount of air being sucked in, it's still controlled by the MAF. People say the stock filter is too small and even too restrictive for the MAF so they use the larger cone filters. Other people say that the restriction is not in the size of the filter, but the temperature of the air, so using the fogged air box allows cooler air to enter the engine.

I think cone filters are best suited towards racing use, as the car is constantly moving at higher speeds and where hot air will not be a restriction as there will always be a source or fresh air.

A fogged air box is better because it provides shielding against hot air from the engine bay while the car is not moving or at lower speeds. It won't be as effective when the car is moving quickly. All depends on what you're looking for.

Bry

Phazer
02-28-2004, 05:16 AM
Originally posted by Autotechnica
You're correct. CAI is usually a cone filter that is placed behind your bumper with piping that goes into your MAF. A fogged airbox is basically just using the stock airbox but with an extra pipe that goes from your bumper or front grill to the side of your stock airbox.

It won't mess up the MAF since it still decides how much air is being sucked in. You could put in a 100cm wide cone air filter and it wouldn't make any difference to the amount of air being sucked in, it's still controlled by the MAF. People say the stock filter is too small and even too restrictive for the MAF so they use the larger cone filters. Other people say that the restriction is not in the size of the filter, but the temperature of the air, so using the fogged air box allows cooler air to enter the engine.

I think cone filters are best suited towards racing use, as the car is constantly moving at higher speeds and where hot air will not be a restriction as there will always be a source or fresh air.

A fogged air box is better because it provides shielding against hot air from the engine bay while the car is not moving or at lower speeds. It won't be as effective when the car is moving quickly. All depends on what you're looking for.

Bry

Nice reply thanks. What about putting a cone filter in but building a cover around it, so it's more or less in it's own "airbox" instead of putting it down by your foglight. That means bigger air intake aswell as cold air, right? So it should be good for town and highway driving. Anyone using BMC or K&N cone filter's? I have read now on a couple of places that engines with them on don't last so long, cause more dirt goes through them, than your normal BMW paper filter.

Cone filter setup that Gizmo is using.

Autotechnica
02-28-2004, 01:34 PM
Originally posted by Phazer
Nice reply thanks. What about putting a cone filter in but building a cover around it, so it's more or less in it's own "airbox" instead of putting it down by your foglight. That means bigger air intake aswell as cold air, right? So it should be good for town and highway driving. Anyone using BMC or K&N cone filter's? I have read now on a couple of places that engines with them on don't last so long, cause more dirt goes through them, than your normal BMW paper filter.

Cone filter setup that Gizmo is using.

A properly designed heat shield would help to sheild the engine's hot air from being sucked into the motor. However, it still isn't as efficient as a real "CAI" which is placed behind the brake duct or foglight. This is the best most efficient option. However, each option has it's own pros and cons.

I'm using a K&N cone filter w/ my own custom heat shield. If you're worried about damaging your motor then just use the stock paper filters with the "fogged" airbox. K&N says that the dirt particles that the filter does not filter just burns up in the motor anyways.

I've used the K&N flat panel filter in the stock airbox as well as a K&N cone filter with heat sheild. On cooler days the cone filter definitely shows more significant gains. On warmer days, with the cone filter, the car would bog and feel like there's no torque. The whole purpose of using the cone filter is that your car should always be moving, and quite fast I might add. That's why cone filter setups are often referred to as "racing filters". When your racing on the track, the car is constantly in motion (hopefully), so there is a constant supply of air being fed into the engine bay. The airbox works better for city driving and traffic jamming conditions. The cone filter works better for higher speed highway driving, reguardless of whether or not you have a heat shield. You can't beat the factory airbox design even if you paid someone $300 to design one for you.

Gizmo has a proper heatshield setup. You want to leave room around the filter, so if you make a heat shield or air box, try not to make it too tight fit.

Bry