CSL Airbox Ducting with Standard M3 Bumper

[jbfrancis3]

Sharing with the group how I created ducting to my Karbonius airbox with the OEM flap using the standard M3's bumper. The goal is to feed air:
- to the snorkel, which is upsteam of (before) the flap on the OEM piece, or just the snorkel itself on the Karbonius snorkel. The snorkel is the beginning section off some airboxes that has a triangular nose.
- to small intake downsteam of (after) the flap, which is on the underside of the Karbonius airbox.

Note other CSL airbox products, like the Evolve and the new Turner airbox with its bellmouth, don't have these multiple inlet places so this post may be of little use.

You can also do this without removing the front bumper/brake duct but it is easier to remove both.

See warning below around this installation with factory power steering (its not proven).

The snorkel up first. We repurpose and modify the standard M3 intake ducting which sits on top of the driver's brake duct.
- We're talking about cutting up part #20, which sits in the top of the brake duct (part#4)
- Cut 1" section out of the duct. Its important to leave a lip on the piece that fits back into the brake duct.







The "lip":


- That lip allows the remaining section of part #20 to slip back over the lip and hold tight.

Here you can see everything installed, the 1" cut section gone, and the accordion section pushed back over the lip.



- One other thing I opted to do is flip around the bottom portion of part#20. Its cut on a slant and from the factory, that slant is rearward facing. Since we're changing the airflow in the brake duct and foregoing the original design, I chose to flip that slant around.
- To do that, you re-notch the brake duct so it can be spun around 180 degrees.

Factory notch on the left, new notch on the right:




So now it looks like this looking into the brake duct from the front of the vehicle:


That's all the modifying. Re-install the brake duct, reinstall part #20, and then install the snorkel. You can also reinstall part#20 onto the snorkel, then install onto the vehicle and snap it back into the brake duct. Light use of heat gun helps part#20 (which is round) fit tightly over the triangular snorkel - you need to force it on. As installed:



Now for the small intake downstream of the flap.

- On the brake duct, cut the small "bulb" off the left side.

Before:


After:


- That's all the modifying needed. This new opening in the brake duct connects to the underside of the airbox using brake ducting which you need to purchase
- You want to use flexible 3" diameter flexible ducting (3 ft length). I recommend the single ply offered by Pegasus: https://www.pegasusautoracing.com/pr...p?Product=3620
- 3" is slightly too big so on this particular Pegasus product, remove some of the inner support metal wire so that you can tightly ziptie the flexible line to the respective connections.

Installed and ziptied to the brake duct


The flexible duct running up the next to the frame. I have a ziptie pulling it tight against the frame rail. With the factory powersteering lines, you aren't going to have much room to run that 3" duct so be prepared to smush it, tie it away, etc. Interference with the powersteering and/or alternator pulley is likely. I did away with the factory lines so it fits well 😛



I don't have a photo of the other side of the flexible line connected to the airbox (too tight) but another large ziptie holds it in place. I also removed some of the inner support wire on that side to make a tight connection.

And now you can see in the brake duct both feeds in place. Done!

[Cubieman]

It looks like I could remove the front most black plastic under-tray deal and get enough access to cut the "bulb" off. I looked last night and it seemed that cutting the bulb off from the top would be quite difficult as well as risky due to the close proximity of the power steering lines.

I have my snorkel set up like you do and have the 3" brake ducting on order. Awesome info, thanks for this post!

[Cubieman]

Thanks jbfrancis3 , I feel much better that the back airbox hole is no longer pulling in hot air right next to the alternator. This cost only $30 for the ducting, the cost of a few tip ties and a few hours labor. I had access to a lift and removing only the belly pan provided sufficient access for this job.

I almost wonder is some sort of screen at the inlet a good idea? I don't think that any water/debris could easily get up into the airbox via the new ducting. Whatever debris would have to go up about 1 & 1/2' then back then go 90° and up again.

[jbfrancis3]

Thanks jbfrancis3 , I feel much better that the back airbox hole is no longer pulling in hot air right next to the alternator. This cost only $30 for the ducting, the cost of a few tip ties and a few hours labor. I had access to a lift and removing only the belly pan provided sufficient access for this job.

I almost wonder is some sort of screen at the inlet a good idea? I don't think that any water/debris could easily get up into the airbox via the new ducting. Whatever debris would have to go up about 1 & 1/2' then back then go 90° and up again.

Nicely done, thanks for the pics with the factory power steering. You might've done a better way leaving yourself slack in the ducting. I re-mounted the airbox cover, cut the ducting down, then zip-tied it from underneath. So I can't remove the cover without cutting the tie from underneath.

Screen wouldn't hurt and be good peace of mind. The filter is there so I'm not worried per se, but you can expect to find a few leaves in there at the next interval. I personally am not concerned about water.

[sc_tr0jan_m3]

this is my next DIY job! sadly the previous owner hacked up the brake ducting so i might have to rebuy that part so i can get a clean fit.

[Cubieman]

Nicely done, thanks for the pics with the factory power steering. You might've done a better way leaving yourself slack in the ducting. I re-mounted the airbox cover, cut the ducting down, then zip-tied it from underneath. So I can't remove the cover without cutting the tie from underneath.

Screen wouldn't hurt and be good peace of mind. The filter is there so I'm not worried per se, but you can expect to find a few leaves in there at the next interval. I personally am not concerned about water.

I also must raise the car, remove belly pan, cut zip tie to frame rail and THEN I can remove the airbox. The slack is no longer there as I made sure that it was safely away from the alternator belt and about 3/4" away from the alternator itself.

Makes for a pain in the ass to split the airbox, but I've got a lift in the garge so not a huge deal.

[RedM3/4]

What was the power steering concern? You don't have PS? I must be seeing something wrong. Nice job either way!

ADS

[jbfrancis3]

I'm running an aftermarket power steering kit from Chase Bays. The hose routing is different than stock, and I have more room along the driver's inside frame rail which is where the added 3" ducting runs.

But that caveat seems unnecessary given Cubieman successfully fit everything with a stock PS setup.

[Exclusivs]

^Thank You! For putting this together! Have been racking my brain of ideas how to fab this up. Really nice write up.


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[Zekarus]

Great thread! Just ordered the Karbonius Airbox and was thinking about this. As I'm getting the Karbonius snorkel I will copy your solution for this but I was thinking about to just plug the small intake. Never heard anyone doing this but isn't the small intake only for idling if you have the flap? Maybe it's just a bad idea but as you already mentioned other airboxes didn't have the small intake at all.

btw this guy just cut of a small portion from top of the air duct

https://www.youtube.com/watch?v=zQ65YkCXUw0

[heinzboehmer]

Great thread! Just ordered the Karbonius Airbox and was thinking about this. As I'm getting the Karbonius snorkel I will copy your solution for this but I was thinking about to just plug the small intake. Never heard anyone doing this but isn't the small intake only for idling if you have the flap? Maybe it's just a bad idea but as you already mentioned other airboxes didn't have the small intake at all.

btw this guy just cut of a small portion from top of the air duct
https://www.youtube.com/watch?v=zQ65YkCXUw0

If you're not running a flap then the idle hole will serve no purpose. It's fine to just cap it off.

[Cubieman]

Yesterday I opened up my air box and removed the (ITG) air filter and discovered a small pile of gravel behind the air filter in the farthest back portion of the airbox.
The gravel/rocks were indeed behind the air filter (scary) but they were sort of trapped between the air filter and the "ledge" it rests on. Some of the pieces were almost bb sized.
I cannot say which hole they came up through and I know the air filter should have kept them out regardless, this may simply be down to fitment of the ITG air filter and/or the Karbonious airbox itself.
In any event, I was wondering what materials I could use to create and air filter for the small hole. I was thinking of stretching panythose over the end of the small hole and then connecting the 3" brake ducting over the top of the pantyhose. I would hope that would prevent rocks getting up there and also still allow sufficient air flow. Any other ideas for making an air filter for this 3" brake ducting > small hole setup?

Also any thoughts on any materials (hobby type foam?) I could use the fill the little gap that exists of the furthest back side of the air filter? I should probably get an OEM air filter and see if it makes a difference.
Does anyone else have a small gap between the air filter and the back side of the box?
The "ledge" of the Karb. box is in this gap I am describing so its not as if this gap makes it a straight shot to the intakes for any debris, but this gravel I found likely got itself into the airbox through this gap.

[jbfrancis3]

Here's what I collected in about 2k miles. Did not bypass the seal which is done at the flange (not the perimeter).

[DI46LO]

This may just be the lazy approach but eventuri sells a scoop that goes into the fog light housing there (no modifications needed)... That's what I use and I think it works pretty well.

https://ind-distribution.com/product...w-e46-m3-scoop

[10figs]

Hi All,

Maybe someone can chime in, I am trying to fit the Karbonius snorkel to OEM airbox duct from the fog light area. I did the opposite and cut the top of the duct back about 2 inches. Still not sure how to fit the triangle shape snorkel end into the duct.

Would I use some sort of flexible tubing or cut it back further and best fit is letting the snorkel sit on it?

Suggestion to cap the small (idle inlet) on the airbox? Painters tape?

Thanks.