home made true cold air intake

[lkchris]

Pay attention to JFP ... someone with experience.

No measured, tested proof has been posted here that the OE air box is "restrictive." No, you can't tell by looking.

A decade or more ago a fairly engineering correct test was performed with a BMW K100 motorcycle, mostly to learn about K&N replacement air filters. The testing found ZERO aitflow difference between
Stock air filter
Stock air filter half blocked off
No air filter installed
K&N

The notions that a German vehicle is poorly engineered or that its performance is "restricted" are pretty dubious. There's real world competition out there on the autobahns, and the factories know it. You're not going to create "supercharging" without a supercharger, but it would sure be cheaper and easier if you could ... and that's the fantasy appeal behind the marketing hype.