R53 Drivetrain :: Airbox Modification How-To
 

A trick borrowed from Porsche Motorsport. This is a variation on the theme, basically allowing more air to the intake. Porsche realized that the stock airbox severely limited air intake to the filter by only having a small bell venturi that drew air into a large airbox with a panel filter. What the Motorsports division realized on the cup cars (which had to have the stock intake) was that if they drilled holes into the box, they greatly increased the allowable mass air flow. This made 5-10 horsepower on the 3.6L aircooled flat six.

The MINI has an intake in the cowling (the area between the bonnet and the windshield) that has one small intake hole into the lower portion (the dirty air side) of the airbox. If you replace the factory element with the aftermarket filters available (any of them will allow this modification to provide benefit), you can greatly increase the flow to the filter by modifying the factory plastic backing plate that separates the engine compartment from this "dead space" area directly adjacent to the factory cowl fresh air inlet.

I can already hear some of the questions, and I'll try to preempt as many as possible, but let me know if you have others.

1. The backing plate is not structural, so the modification has no safety ramifications in the event of an impact.

2. The dead space is not critical as far as temperature is concerned. The transfer of engine compartment heat to this area is negligible anyway.

3. I washed and waxed the car right after completing this mod, and no extra water was in the engine compartment - most of it comes from the intercooler inlet.

4. There is a small increase in supercharger whine (above that caused by the intake change) but nothing intrusive at all.

5. Be certain to follow the instructions and remove the partition (backing plate) completely before modifying, as there are brake lines directly behind the plate.

Time required
about an hour - less if you are familiar with the filter set-up.

Tools required
small standard screwdriver
phillips head screw driver
10mm socket with extension
8mm socket
#25 torx
15mm wrench
2" holesaw
hand drill or drill press (drill press makes it a bit easier)
new hose clamp - same size as the one that came with your filter kit

Step 1: Locate the airbox and become familiar with it's surrounding attachments, as well as the partition itself and its attachment points.

http://www.imagestation.com/picture/...c/fcde3d48.jpghttps://www.northamericanmotoring.co...ta/741/3w1.jpg

You can see the partition (the black piece) behind the airbox.

Step 2: Remove the weatherstripping. It just pulls off and pushes right back on.

http://www.imagestation.com/picture/...e/fcde3ce7.jpghttps://www.northamericanmotoring.co...ta/741/3w2.jpg

The stripping is removed in this picture and laid on the cowl. It came off of the plate we'll be modifying right in front of the brake reservoir. You can also see the stock small inlet at the bottom of the airbox in this shot.

Step 3: Remove the ECU cover. The ECU is attached to the lower portion of the airbox, and we'll be removing it to gain access to the lower attachments of the partition.

http://www.imagestation.com/picture/...2/fcde3c9a.jpg

Step 4: Remove the ECU plugs. Look at the ends of the plugs. They have a pull tab that disconnects them form the ECU. Pull the tab all the way out and it will do most of the work for you.

http://www.imagestation.com/picture/...9/fcde3c2c.jpghttps://www.northamericanmotoring.co...ta/741/3w4.jpg

The plug is removed in this shot. You can see the pull tab which is in the extended position in this picture. You also will pull the grommet that keeps the ECU plug attached to the partition.

http://www.imagestation.com/picture/...6/fcde3ba8.jpghttps://www.northamericanmotoring.co...ta/741/3w5.jpg

This is what the ECU will look like with both plugs removed.

Step 5: Remove the battery terminal from the air intake. This differs slightly from model to model depending on which you have, but it is painfully obvious how to do it when you locate the terminal.

http://www.imagestation.com/picture/...b/fcde3b31.jpghttps://www.northamericanmotoring.co...ta/741/3w6.jpg

Here the terminal has been removed from the air intake heat shield.

Step 6: Remove the passenger side airbox bolts using the 8mm socket (or 10mm if you have the Pipercross). There are two, a top and a lower. These also attach the partition we are working with to the center partition.

http://www.imagestation.com/picture/...2/fcde3ada.jpg

Here, the heat shield has already been removed, but the bolt holes are clearly visible to the left.

Step 7: Remove the partition plastic screw in the upper driver side corner. This is a phillips head screw. Note: the early production models do not have this screw, but the partition is bossed for it.

http://www.imagestation.com/picture/...f/fcde3a9a.jpghttps://www.northamericanmotoring.co...ta/741/3w8.jpg

There is a screwdriver in place in this picture.

Step 8: Remove the front 10mm bolt on the lower airbox.

http://www.imagestation.com/picture/...3/fcde3a3c.jpg

This picture shows the bolt being removed. It is directly in front of the fuse panel.

Step 9: Remove the clamp that holds the "snorkel" to the intake tube for the lower airbox. The best way to do this is with the small standard screwdriver. Put the blade into the crimp of the clamp and pop it off. It will then just pull apart and come right off.

http://www.imagestation.com/picture/...0/fcde39d0.jpghttps://www.northamericanmotoring.co...a/741/3w10.jpg

Step 10: Remove the #25 torx bolts that hold the forward part of your aftermarket intake down to the lower airbox. With the Pipercross and Rogue/MINI-Madness filter, these hold the forward part of the heat shield down. For the BMP, these are the forward mounting bolts.

Step 11: Remove the #25 torx bolts that hold the intercooler cover down. The rear bolts are longer for the reinstalling phase.

http://www.imagestation.com/picture/...4/fcde398a.jpg

http://www.imagestation.com/picture/...6/fcde3942.jpg
https://www.northamericanmotoring.co...a/741/3w12.jpg

Here's the intercooler without the cover - pretty cool!

Step 12: Pull the airbox stock "dead space" intake hole grommet through the hole and pull the lower airbox back slightly. This will remove it from the lower mounts shown here:

http://www.imagestation.com/picture/...b/fcde38f2.jpg

Step 13: Remove the lower portion of the airbox by pulling up and out, using caution for the wire bundle that was attached to the same forward 10mm airbox bolt. If you move this wire bundle out of the way, then hold the intake hose out of the way, the box should pull straight out.

Step 14: This step is only for rally light equipped cars. You have to remove the hot wire to the fuse panel by removing the fuse cover and unbolting the 10mm bolt. Then fish the wire through the partition (disconnect the battery first).

http://www.imagestation.com/picture/...4/fcde38bc.jpghttps://www.northamericanmotoring.co...a/741/3w14.jpg

Step 15: Remove the lower airbox mounts by unscrewing the base 15mm nuts under the rubber mounts.

http://www.imagestation.com/picture/...d/fcde386c.jpg

Step 16: The part all of this work was for! We can finally pull out the partition. It just wiggles right out. Here's what it looks like once out:

http://www.imagestation.com/picture/...8/fcde3824.jpg
https://www.northamericanmotoring.co...a/741/3w16.jpg
http://www.imagestation.com/picture/...6/fcde37ba.jpg
https://www.northamericanmotoring.co...a/741/3w17.jpg

Step 17: Now the mod. You will take the 2" holesaw and make six holes in the partition above the line of the lower airbox cover, so the intake air is available to the filter. This is easier with a drill press, but you can do it with a hand held as well - just be steady. Here is the finished product:

http://www.imagestation.com/picture/...1/fcde373e.jpghttps://www.northamericanmotoring.co...a/741/3w18.jpg

Now reverse the steps for the reintstall of the partition and lower airbox. This is when you need the new hose clamp - for the "snorkel" to intake hose connection. Here's what the completed project looks like in the car - subtle, but trick!

http://www.imagestation.com/picture/...f/fcde36d8.jpg

The disassembly car has the Pipercross intake, while the finished project car shows the MINI-Madness intake.

If anyone has any questions, feel free to call me at the shop. It may benefit others if you post your question on the thread, too.

Randy Webb
Owner, Webb Motorsports
randy@webbmotorsports.com
720-841-1002




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MINI-Motorsport

Randy,

:cool: Yet another of your great step-by-step write-ups! :cool:

Driving around this afternoon and this evening with the new holes in the airbox, there is now a slightly more pronounced supercharger whine at WOT (wide open throttle). Pretty cool actually.

Thanks again for sharing some of your Porsche background with your MINI breathren. :cool:

Thanks Dave!

I'm starting to wonder how much of the "unfair advantage" I should be sharing with guys that I'll be running against :wink: :lol:

[quote]Originally posted by RandyBMC:
I'm starting to wonder how much of the "unfair advantage" I should be sharing with guys that I'll be running against :wink: :wink: :lol:

Very nice...you guys have been busy! :smile:

ficcion,

We had to find a way to keep up with those Azenis tires :lol:

I'd be glad to help you out with this mod. As TeamMINI, we really should be on an "info share" mentality. As for those Bimmers - they can fend for themselves!

Randy

The partition is available from MINI for those who would like to have the option to return to stcok. Prices fluctuate from dealer to dealer, so check with your local parts department.

Hey Randy,

Any reason why we should drill 6 circles as opposed to dremeling out one large rectangle?

>>Hey Randy,
>>
>>Any reason why we should drill 6 circles as opposed to dremeling out one large rectangle?

Probably for structural rigidity. Then again, it could be for the neater look.

X2

I don't think there would be a problem with dremeling out a large rectangle. That partition supports the weather stripping across the back edge of the bonnet, so I can't really see that there is a strength/stiffness reason not to open it up.

Great report & demo! MCOwill (if not already) be the best sight for the Mini community.

Albert,

I don't think it is very structural, but it would be a little flimsier to cut out the whole thing. You also lose the cool value. The holes look very motorsportish and provide close to the same airflow that removing the entire area would. There are also eight holes total - two secret ones along the side that you can see if you look at the last installed photo. You wouldn't want to remove that much material by just cutting it out, because you would lose some of the strength that the curve in the plastic makes, so you would end up having to drill those holes even if you did remove a rectangle.

Hope that helps!

Randy

Thanks Randy. :smile:

Anyone know the part number to the piece?

Thanks Randy - Awesome job on the article and pics. With a few days off this week, but not much money this is one of those mods I'll take on with all the information you provided.

sndwave,

Great! Just make sure you have an aftermarket intake. If you do the mod with the stock airbox, there isn't anywhere for the additional air to go, so it won't make any improvements.

Randy

i've been considering a similar mod but wanted to test the airflow/pressure in the windsheild vent area. It seems possible at speed that the air moving over the hood and up the windscreen might create a negative pressure in the vent. this would perhaps augment suction through the normal intake but not directly supply any air to the filter box.

any comments?

Thought was given to this. A simple string test (like gliders use for yaw strings and stall warning) shows the flow doesn't change significantly over this area. I would love to have the equipment to test the area inside the cowl, but don't at this time. If you are able to secure the equipment, let me know. You would have to do the test before and after the mod, as the dynamics change after the flow has been altered by the holes for the intake.

No dyno tests have been done yet, but strictly seat of the pants says there is a definite increase in power, especially in transitional RPM ranges. The noise of the supercharger is much greater - a whole different sound than just the intake provided - and it's very grrr baby!

The Porsche had a similar set up in that the flow of air above the engine was also in the flow over the car, which could be assumed would create a boundary layer that could induce a low pressure. Since the factory (which does have access to the pressure testing equipment) used this mod in a performance application, the pressure change must not offset the greater intake mass available.

As soon as the dyno is secured (things are tough to arrange over the holidays) testing will show the numbers. Like I said in the Porsche (which is a totally different motor and engine management and intake) they were getting 5-10 hp gains.

Let me know if you have any other questions.

Randy

IMO one thing that dyno's have been inherently bad at is replicating airflow over the car. Some fans pointed at the car (hood up or hood down) don't produce nearly enough fresh air flow over the car to even replicate say a 30 mph wind (i.e. what the car would see at 30 mph when driving).

my little project this week is to fabricate a tidy little scoop to fit over the vent area (facing forward). I just happen to have some titanium sheet left over from another application and the natural color matches MINI dark silver very well. I'll keep you informed.
also, I have been meaning to get at those extra holes, but I think I can do it with a chassis punch without removing the plasitc from the car.

I resent the BMW bashing on this board. I have an M3 as well. Can't we all get along? :lol:

Great write up. I may have to do this simple mod. If possible please update us with the dyno info. That would be greatly appreaciated.

jlm,

Be very careful doing anything with this partition in the car. The brake lines run directly behind it, right where you want to make the holes.

I'll be very interested in seeing the titanium intake if you get that put together. There may not be too much of a need though - wait until you feel the difference!

Randy

[quote]I resent the BMW bashing on this board. I have an M3 as well. Can't we all get along? :cool:

>>IMO one thing that dyno's have been inherently bad at is replicating airflow over the car. Some fans pointed at the car (hood up or hood down) don't produce nearly enough fresh air flow over the car to even replicate say a 30 mph wind (i.e. what the car would see at 30 mph when driving).

I've said this for forever, but nobody seems to listen =/ Blue Thunder (on MINI2) has talked about how the pressure under the car at speed is very important to the performance increase, as it offsets some of the potential warm air induction. What I really want it for someone to both dyno AND g-tech and see those numbers. Either that or install a dyno in a wind tunnel, but i think i'm dreaming for that one....

Speaking as someone with an aerospace engineering background, I'd love to see that too.

Randy,
Your work is well timed. I was planning on doing something just like this when my Mini Madness Air Intake came in (next week?). I was wondering why no one had done this before, it seems so logical.
Thanks for documenting the process so well. You have taken a lot of the guesswork out of it for me!
:razz: