When you say torque do you actually mean that??
Normally the quest is for power (BHP) and along with that they'll be an increase in torque - but from what you've said you want more raw pulling power over pure BHP correct
If that's the case it's really not gonna be cheap - most mods are there to either increase air / fuel or get the car using higher revs to breathe better. Torque is completely different and usually comes from an increase in capacity - so from a say 1800cc to 2000cc, or as you say an increase in diameter in the inlet track; but this in turn pushes the power further up the rev range.
I could waffle on for ages - but bottom line is, is this what you're really after??