Thanks for the writeup. That's good stuff.

I assume that it's $160 for your M5 since you have dual intakes ($80 per side)?

If I'm not mistaken, the left airbox on the E39 M5 is about the same spec as the airbox on the E39 540i which is the equivalent to the X5 4.4i. I should be able to take your DIY and run with it.

I have a couple of questions.

What was the part # for the filter?

What's the size of the aluminum tubing? I have some old 2.75" tubing in the garage from an old Toyota CAI unit already bent at 45". Since you cut off 13" from the 15" tubing, am I right in stating what remained was 2" at the apex?

The aluminum tape is used to ask as a gasket between the aluminum tubing and the intake housing? Are you trying to seal the box? I see where you have it wrapped around the tubing until "it fits tightly enough..."

What's great about this mod, it's quick, easy, cheap, and it appears to be easily reversible. It probably would yield less than 12HP on a 4.4i as compared to your M5, but I'd be happy to get 8 or so HP from my 4.4i from what is apparently a very inexpensive mod.

Thanks, TQ2K!