I have repped of the forst part of the tube. I saw some improvement on thretle response. Then I thought a 4cm hole seems kind of small for a 2lit engine, so I drill a 8cm hole ( its a speaker's bass reflex tube) and saw some more (small) improvment, then, reading a post on snorkels and how cool intake air is goor I added the aluminium tube wich is 10cm diameter ( 10 cm is the "flange" of the bass tube) so here are some picks.
Evaluation? Hmmm not much at low thow it seems to rev a little faster, notisable from 3,500. I think that all you with KN filters you may see more improvment.
Here are some photos



Its not over yet since I have to relocate the radiator expansion bottle because now the alu tube is severely bented to pass and not at fuul diameter