Airbox or no Airbox?

[sperkins]

I upgraded my intake & filter to an MS unit. Until recently I was running the airbox with lid, but wondering if it makes any difference if I run the system without the airbox? I know BMW engineers spent a lot of time creating a true cold air system. I'm pretty much using the m3 for track days only now, so by opening up that side of the engine, i'm hoping the outside air will vent the engine bay, AND force enough air into the intake during the session. FWIW, I opened up the hood vent on the order side as well. Is there enough outside air coming into the engine bay at track speeds to still give the intake the cold air it needs, or should I go back to the airbox?

Am i looking at a negative pressure situation with all of that air swirling around under the hood?

If i'm being honest, I really like the look without the box, (and the sound) but will absolutely reinstall it if that is still the best for track performance.

[Brandoch]

Originally Posted by sperkins

I upgraded my intake & filter to an MS unit. Until recently I was running the airbox with lid, but wondering if it makes any difference if I run the system without the airbox? I know BMW engineers spent a lot of time creating a true cold air system. I'm pretty much using the m3 for track days only now, so by opening up that side of the engine, i'm hoping the outside air will vent the engine bay, AND force enough air into the intake during the session. FWIW, I opened up the hood vent on the order side as well. Is there enough outside air coming into the engine bay at track speeds to still give the intake the cold air it needs, or should I go back to the airbox?

Am i looking at a negative pressure situation with all of that air swirling around under the hood?

If i'm being honest, I really like the look without the box, (and the sound) but will absolutely reinstall it if that is still the best for track performance.

You now have a hot air intake.

[a5m]

^ this. Put the Airbox back on.

[tom @ eas]

Originally Posted by Brandoch

You now have a hot air intake.

+1.

The images without the airbox lid are for illustration only, you should reinstall the airbox & lid, otherwise - this is just sucking up hot engine air.

[Scrippy]

I agree, hot air is not what you want. Cold air is denser and will provide better power per stroke. If you wanted to feed cool air in the engine bay, why not run some intake hoses? Without pass through ventilation your and my option will not do much as the air cannot escape out.

[tom @ eas]

The stock airbox is very efficient, taking advantage of (3) air inlets. It's the intake tract & filter media that is the bottleneck of the system.

Removing the airbox to run an open element intake would defeat this.

[sperkins]

Alright, alright, I get it. Airbox is back in. I appreciate it boys!

[tsk94]

It probably sounds great without it, but you'll 100% be losing power when temps go up.

[Ximian]

Throwing a curve ball here -

I have a vented hood and I've tried it without the top of the airbox (since the bolt holes are stripped anyway) without any issues. A reason I want to get rid of the bottom part of the airbox as well is that most of the air is coming in through the lower part of the front bumper and I'll have a vent as a path out. It would get rid of a lot more heat in the engine bay. I've seen an E46 M3 with essentially this configuration of getting air through a lower part of the front bumper, but without a vented hood.

I talked to a shop foreman at a track event about it and he suggested a test. Do some pulls at a drag strip and measure the acceleration, top speed, and intake air temperatures to get a baseline. Then remove the airbox and do the same. I haven't done this yet but would like to try at some point.

[tsk94]

If you can monitor IAT, it's worth a try.
Nothing bad can happen, at worst you experience higher IAT and lose some power, but beyond there's no risk. Worth a try to see, what the heck.

[Redd]

When the car is moving and there is airflow, I doubt there is much difference with or without airbox. However when you're parked/stationary the heatsoak will be terrible without airbox. Vented hood or not, engine bay temps climb rapidly when the car is not moving.

If you want more noise you can try removing the lid and sealing the lower airbox against the hood using some rubber door edge seal.

[omgzirra_exe]

Originally Posted by Ximian

I talked to a shop foreman at a track event about it and he suggested a test. Do some pulls at a drag strip and measure the acceleration, top speed, and intake air temperatures to get a baseline. Then remove the airbox and do the same. I haven't done this yet but would like to try at some point.

I like this shop foreman. I always advocate a drag strip to verify engine performance gains over track times.

[Ximian]

Originally Posted by omgzirra_exe

I like this shop foreman. I always advocate a drag strip to verify engine performance gains over track times.

Drag strip for consistency and checking how pressure builds up in the engine bay at various speeds. Also the drag strip specifically is because that is a track layout we had available.

I wasn't going for engine performance gains but rather engine cooling improvements.

[M3SQRD]

Without airbox, I’d extend the end of the front lower bumper inlet tube (#3 in above picture) so the cool air is concentrated onto the underside of the air filter. Without the extension, you’ll lose velocity and the air has sufficient distance to spread and spill around the sides of the air filter.

The Eventuri intake on my f82 is basically open to the engine bay (stock closed airboxes are completely removed) yet I still netted a repeatable 5-8 whp across all rpm and a peak increase of 10 whp. Waited 15 min between two pulls to see if heat soak would affect gains. It did not. These pulls were used as the baseline before installing GTS level power and stage 1 ecu tunes. However, I’m well aware of the loss of power from heat soak on my two e92 M3s so the f82 results may not be representative of the results from a s65 with an open air intake.

[omgzirra_exe]

Originally Posted by M3SQRD

The Eventuri intake on my f82 is basically open to the engine bay (stock closed airboxes are completely removed) yet I still netted a repeatable 5-8 whp across all rpm and a peak increase of 10 whp.

are the F8X intakes wet filters or dry filters? wet filters typically have lager openings but require oiling to keep the filter from sucking in dust. but net higher performance gains over dry.

[M3SQRD]

Originally Posted by omgzirra_exe

are the F8X intakes wet filters or dry filters? wet filters typically have lager openings but require oiling to keep the filter from sucking in dust. but net higher performance gains over dry.

Dry

[tdott]

Hot air intake, I wouldn't do it.

Add hood vents if that is what you want.

[roastbeef]

what you can't see, is how much that intake neck is going to be bouncing around without the support of the lower part of the box. i'd bet it doesn't stay on as intended.

secondary to that, but the box back on. it is probably the best thought out intake of any vehicle that exists.