Norfolk: To be honest, i cant say, it was only ever run on the track as it was a cup racer. so, i cant compare really, Fuel consumption will go up, and by quite a heafty amount.....but, if you want power, you really cant complain.
Rob: no head of them in particular but the idea is old.
Basically, they have gone about getting the increase in torque etc by increasing the inlet tract length. Old stuff. As for the rifled bore, its again old stuff and has been proven not to be worth the hassle. when you spin the air, you get 2 axis of inertia, one in the direction of flow, and one off the plane of the spin.....which only leads to loosing fuel out of suspension......BAD.
Most popular form of tract texturing now is the gold ball dimple style texture. This is only really applicable to top power F1 motors and similar. THe effect causes mini air spheres at the dimple location, and aird boundary turbulance to top moving air and fuel from actually touching port walls.
Another bad problem with spacers is that you move the injector position. You move it further from the inlet valve, reducing throttle response and increasing dropout at low low rpm. Easiest solution is to jsut use longer trumpets.....job done.