Well, yesterday I cut a hole into the airbox lid, and glued a 65mm (2.5") PVC pipe into it... as expected, this had no effect on either the performance or the sound of the car...
Firstly, I'm now wondering.. what is the bottleneck in the system? The pipe off the bottom of the airbox has a 65mm opening into the airbox, and the pipe itself has a minimum diameter of 65mm, and it then feeds through the LPG mixer, into the throttle body, which I assume is all 65mm as well. In order to get greater airflow (if that is even what I need), I assume I would have to replace that tube, the bottom of the airbox, and also the throttle body..?
Well, that probably wont happen for a long time, so I'm going to plan 2:
**** performance, lets make some cool induction noises
I figure that the 65mm tubing is a good starting point.. what sort've crazy contraption would anyone recommend I insert into the pipe, to create some kind of (loud) turbulence, preferably in the form of a deepish roaring noise? All I get at the moment, is a high-pitched whistle when I revv it out to 4500rpm, but this is only just after starting, as soon as the engine bay gets warm, this noise dissapears.
Apparently the noise you get from a pod filter is due to the way the pod filter forces the air into a spiralling effect (kind've like a tornado), and this also causes the air to move faster, increasing response time (not an issue.. the LPG is INCREDIBLY un-responsive, due to years of neglecting to service the vaporisor)... perhaps I could stick some kind of spiral into the 65mm tube?