So the MAF tube from a BMW 540i has been recommended in this thread as a good choice when installing a 987 airbox but can anyone tell me the diameter of that MAF housing? Is it the same as the OE 986 tube built into the 986 airbox? I'm trying to make sure it will work with the 00 986S ECU and 996 74mm throttle body without going lean. The MAF I'm referring to is Bosch #0280217814 from a '00 BMW 540i among others.

There's a lot of good info in this thread but much is outdated and/or confusing; I'm going to start a more current thread and am in the process of determining the best info to put in that thread. My goal is to list the parts at the best current prices and availability to help anyone trying to complete the 987 airbox mod. I'll post a link once the new thread is created.

Thanks to all who have created this thread and would love to hear any updates they may have regarding their experience since some of these posts date back to 2012!

I did this with my project S.
I used the 987 MAF sensor but neither elbow would work so I had to make one using a silicone elbow. I was also advised to get a 996 ROW tune since I added headers (stock is beyond abysmal, might as well be a Model A!) and block-off plates for secondary air injection. I never got to try it as engine 2 locked up a mile from the shop helping sort it. Building engine #3 now so hoping to see how this works later this summer!

"Is it the same as the OE 986 tube built into the 986 airbox?"

no