Airbox intake tube measurement

[tjts1]

I have an M42 car. Looking at realoem, I noticed that the M20 uses the same size filter and AFM but the lower airbox and intake tube part numbers are different. If anybody has an M20 airbox intake tube on hand (Part 12 pictured) or the lower airbox,

http://www.realoem.com/bmw/showparts.do?model=1413&mospid=47322&btnr=13_0323&hg=13&fg=20

could you please measure the inside diameter at the beginning and end of the tube. The M42 tube has an inside diameter of 2.1" at the beginning and 3.1" at the back where it connects to the lower airbox. I'm trying to see if the M20 tube and lower airbox is a worthwhile investment for the M42.
Thanks for you help.

[nando]

it's not going to make any difference - the M42 isn't airbox restricted in the least.

[tjts1]

I don't think the airbox is restrictive either. But the 2.1" opening on the tube going to the airbox could be improved and in order to fit the M20 tube (if its larger) I would have to use the M20 lower airbox. I did some pressure testing the other night in 40f weather. Full throttle in second gear at 6000rpm, I found 5" of vacuum in the bottom half of the airbox. If the airbox isn't causing a restriction, something else is and the 2" tube is a good candidate.