Turns out the air intake box on the M roadster is slightly different than the air intake box on the 2.8 liter Z3. The difference stems from the fact that the M roadster has an additional air intake “snorkel” that is connected down to the hole on the front bumper where the 2.8 liter Z3 fog lights are installed.

I was curious to see how BMW redesigned the air intake box to account for this additional air intake. Dissecting the M air intake box might also be informative to 2.8 owners who are looking to increase the airflow to their roadsters. It appears you could even retro-fit the M air box into a 2.8 and install your own snorkel, but I’ll let a 2.8 owner try that one.

First step was to remove the air filter so I could see inside the box. Two plastic clips hold the filter housing in place. After the clips are unclipped, the entire filter housing slides out (FYI: this is also how you replace the filter). I believe I’m still on my factory filter and have over 11,000 miles on my M roadster. The filter still looks fairly clean, but I knocked some dust off since I had it out anyway.

Once the filter is removed you can look into the wide slot on the top of the air box. The following pictures are of inside that open slot, but because it is dark in there it is difficult to make out what you will be seeing. Just remember you are looking down into the now open slot where the air filter used to be.

First notice the debris that had accumulated in the air box. It was mostly sand and dirt, but I did find one pebble about 5/6th the size of a dime (guess this is why we have air filters). But the important thing to notice in this picture is the tube inside the air box. This tube is what carries air INTO the air box.

Getting the camera positioned just right, you can actually find the right angle and see down into the air box, through that air tube, down the snorkel, to the bumper and catch some daylight. I’m sure this is probably the path that nearly dime sized pebble took, but the point is it is also the path that a LOT of air took.

The other air intake position is just to the left of the driver’s side headlight. Although this area is not directly exposed behind the kidney grill on the hood, it is pretty close and should catch a lot of incoming air. This air intake is identical to the air intake on the 2.8 liter Z3, although in the 2.8 it is the sole air intake. In the M this intake works in addition to the other one. They are both connected to the air box via the same tube I showed you inside the air box (so there is a “Y” connection somewhere just outside the air box).

Looking back in the air box (remember the air filter is removed in this picture) you can see a second tube that would normally be on the other side of the air filter. This tube moves air from the air box into the engine. Just out of frame but to the right of this picture is a air flow meter that monitors the airflow and passes the information onto the roadster’s CPU.