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


Once you remove all six clamps, you’ll have two more vacuum lines to pull underneath, and one bolt securing this bracket that secures the intake plenum.  Remove that, and the intake manifold should pull off freely.

The two vacuum lines you see being held, plus the one in the foreground, are the three that go onto the intake plenum.  However, as the air that goes into our motor is being monitored by a Manifold Air Pressure (MAP) sensor, instead of the factory HFM—thanks to the AEM Infinity EMS—and the fact that the car's throttle bodies are after the airbox, means we don’t even need to connect these to run the car.

Here is our engine with the intake manifold removed.  Believe it or not, thanks to the MAP sensor multi-throttle body setup, our engine will actually run just fine this way.  After all, it’s only missing the air filter at this point.  And we’ll actually show you what it makes on the dyno like this on Page 5 as well.  Compared to the E36 M3, let alone an E46 325i, removing the intake plenum on an E46 M3 is so much easier.  A lot of this has to do with not having to remove the individual throttle bodies (in the case of a 325i, removing the single throttle body is no fun).

While removing the intake manifold on an E36 M3 can take an hour or two, and double that on a 325i, taking out the same piece on this car now only takes us about 8-10 minutes, including removing the strut tower bar!


To cover up those exposed lines, we went ahead and ordered a couple more K&N breather filters from  The big one here goes to the idle air control valve.

With our new, huge cone intake filter, these breather filters will compliment the engine bay nicely.

So now we get to see how much power this M3 makes without the airbox and zero restrictions all together.  How much of a gain do you think we'll see?  Find out on the next page.

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