Dyer,
Contrary to popular belief, you can get a noticable gain in both torque and bhp from an N/A with this economic DIY induction mod.
Ram induction
1 x 4" plastic soil pipe elbow
1 x 4" plastic to 4" clay rubber adapter, comes with stainless jubille clip. (6-4 ram pipe)
Filter box
Off cut of 2mm aluminium
3" K&N (or A.N. Other) filter
Door seal rubber (from breakers)
Bubblewrap strip (plumbers pipe lagging)
Heating engineers aluminium tape
Plenum
1 x 75 - 102mm 90o rubber or silicone elbow
1 x 102 - 102mm 45o rubber or silicone bend
1 x 102 - 75mm 45o rubber or silicone bend
Glue (I found Loctite silicone the best)
Shrink tube (4")
Bubblewrap strip (plumbers pipe lagging)
Heating engineers aluminium tape
2 x 3" hose clips
And breather filters for the right rocker cover and crankcase.
It sounds a bit 'Blue Peter' yet gives a definite power gain, sounds a treat and looks good too
Pics in 'my garage', (link below) and there are some snaps of the induction system in various stages of construction/installation, here and there on pages 2 & 1 in the 'Evolution' album in my profile.
Take a look.