S50 Airbox Installation
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. The S50 "Intake Muffler" assembly (13711405279) is mostly the same as the S52 assembly, with the exception of a mount that accommodates a Bosch 3.5" HFM and 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:
The crankcase ventilation port was easily sealed with a 7/8" high temperature black plastic plug and a dab of Three Bond 1211 for insurance.
A new left brake duct was fitted to replace the flex-tube connection that was missing from the duct modified for the Dinan CAI:
I was also missing the ducting that fits behind the left headlight (Air Duct Front Left 51712491033) 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:
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 I'm probably going to go back to an OEM S52 intake boot to isolate the HFM from engine torque and vibration:
I stuffed the S50 airbox with an OEM paper element; it's the same air filter element for all Z3 engines. I like MAHLE air and oil filters, which are often what you will find in a "Genuine BMW" branded parts box. Butt dyno testing reveals the same if not better performance as 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 hoped that dicing a circular chunk out of the hood insulation would provide enough room for the HFM connector, but the connector and the front corner of the airbox were still rubbing:
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 clearance, and there was still the issue of the front corner of the airbox contacting the hood insulation. I also have not had any luck finding an aftermarket rubber accordion section to mate with the less than flexible Cosmo intake boot that I was happy with, 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, the HFM was given a 180° rotation, and an OEM S52 intake boot went back in place with a Dinan adapter to mate with the 3.5" HFM. Fortunately, there was plenty of clearance for the protruding HFM electrical connector and the wiring harness was long enough to accommodate the rotated position:
Rotated HFM, S52 intake boot, and the 3.5" to 3" adapter that was part of the Dinan CAI installation:
No noticeable difference in performance going back to the OEM boot, and while I'm mildly concerned that the HFM electrical connector is now exposed to more heat and potentially more moisture, I think it'll be fine. The hood clearance issue appears to be solved and the HFM will probably live a longer life attached to the flexible OEM intake boot rather than the relatively rigid silicone Cosmo Racing boot.