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S50 Airbox

    I finally got around to replacing the Dinan CAI with a proper airbox; details of why I was not particularly happy with the Dinan CAI can be found here. The 3.5″ HFM and associated Dinan tune complicated matters, preventing the installation of an S52 airbox without substantial modification to the 3″ HFM mount on the OEM airbox , so I went Euro and fitted an S50 airbox.

    Pre-2001 Z3 M cars sold in places other than North America were equipped with the 316 horsepower S50 engine, and while the S50 “Intake Muffler” assembly is very similar to the S52 version, it is designed to mount a Bosch 3.5″ HFM. There’s also an extra port for the S50 crankcase ventilation system. Another difference is the S50 ‘box does not have the protruding Helmholtz resonator that’s tacked onto the S52 ‘box:

    European Z3 M S50 Airbox

    The crankcase ventilation port was easily sealed with a 7/8″ high temperature black plastic plug and a dab of ThreeBond 1211, which is my favorite automotive silicone sealant, for insurance. Yamabond is excellent too, I always have a tube of 1211 or Yamabond in the garage.

    A new left brake duct was fitted to replace the flex-tube connection that was missing from the duct crudely modified to accommodate the Dinan CAI:

    Z3 M Left Brake Duct

    I was also missing the ducting that fits behind the left headlight that pulls air from the left side of the radiator and connects the brake duct flex tube to the airbox; it’s the same part for both S50 and S52 Z3M cars. The duct and two associated headlight bulb access covers are shown below:

    Air Duct Bits

    The S50 airbox fits pretty well, but the S50 manifold inlet is positioned lower than the S52 throttle body and the HFM mount on the S50 Airbox places the HFM outlet at a slight downward angle, also a bit off-center from the S52 ASC inlet, so a dose of minor HFM to ASC+T cut-n-paste was required. I diced up the Cosmo Racing silicone boot I installed awhile back, and added a chunk of mandrel-bent 3.5″ aluminum tubing to make the connection, but ended up going to go back to an OEM S52 intake boot to isolate the HFM from engine torque and vibration:

    S50 Airbox Installed

    I initially stuffed the S50 airbox  with an OEM paper element;  it’s the same air filter element for all Z3 engines.  I like MAYLE or MANN paper air filters, which are often what you will find in a “Genuine BMW” branded parts box, but for a reusable, higher flow option, I strongly prefer AEM “DryFlow” filters rather than the ubiquitous K&N aftermarket filters. The AEM filters are washable and reusable without the need for filter oil. Over-oiling a K&N filter can ruin a Hot Film Mass Airflow Sensor (HFM). AEM 28-20070 is a direct replacement for the BMW 13721730449 filter element. Butt dyno testing after the S50 airbox swap revealed the same if not better performance than the Dinan CAI.

    With the hood closed, the only noticeable difference is less intake noise, but that’s fine, I still have plenty of Dinan exhaust rumble.

    Speaking of hood clearance, I knew that it was going to be tight between the S50 airbox / HFM Electrical connector and the hood, and found that the HFM- electrical connector was rubbing the hood insulation.

    The S50 airbox and 3.5″ HFM are keyed to each other with tabs and two screws, so I couldn’t easily rotate the HFM a few degrees for more hood clearance. I also have not had any luck finding an aftermarket intake boot better than somewhat rigid Cosmo part, so I massaged the airbox mounting tab slot to allow the airbox to sit a bit lower, but still properly mate with the inlet ducting, rotated the HFM 180°, and fitted an OEM S52 intake boot with the Dinan adapter to mate with the 3.5″ HFM. Concerning OEM S52 M Roadster intake boots; there are two flavors, one for cars equipped with “Automatic Stability Control plus Traction” (ASC+T) like mine, and one for those without the system. ASC+T adds a module in series with the throttle body, requiring a shorter intake boot. Fortunately, there was plenty of clearance for the protruding HFM electrical connector and the wiring harness was long enough to accommodate the rotated position:

    OEM Boot and Rotated HFM

    One of the most common BMW intake problems is a dry-rotted or torn intake boot, it’s worth inspecting yours and replacing it if it appears sketchy.

    Rotated HFM, S52 intake boot, and the 3.5″ to 3″ adapter that was part of the Dinan CAI installation:

    OEM ASC+T Intake Boot, Dinan Adapter, and Rotated HFM