Project E46 M3: Part 11 – Castro Motorsports air box installed and dyno tested!


Since the filter would not fit down behind the headlight, I had to fight for every millimeter.  Literally.  I continued by shaving off one of the engine bay tabs behind the driver's side headlight, which really goes unnoticed.  In fact, I'm worried even mentioning this will stop half of our readers originally contemplating this install to not go any further.  But it's really not that big a deal.  Relax already!

The rest of the filter-fitting process had to do with simply shoving the filter up as high as possible, and massaging the intake back and forth onto the runners at the same time.  After several minutes of fighting the alignment between the intake runners and the throttle bodies, I discovered that it was much easier to do with the silicone couplings left on the throttle bodies themselves, not the airbox.


We’re left with this crankcase breather line—which comes from our Radium Engineering oil catch can featured in Part 3—that used to go on top of the intake manifold. 

We have two choices.  Either route route this line back into the intake manifold by drilling it, or route it to atmosphere.  We chose the latter, and routed it to the bottom of the car by adding another line to it. 

Here’s a look at our Castro Motorsport intake plenum installed, with the crazy-big cone air filter that is almost as big as a racing helmet.  It barely fits.  If you look closely, you can also see a small piece of double-sided foam tape  tape we used between the top of the plenum and the strut brace, since they were coming into contact with each other.  So far, after now 5 months of operation with this manifold on, we haven't had a problem.

Find out if all this work was worthwhile on the next page!

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