For "performance" on a budget I'd get a panel filter and put a DIY cold air feed on there,
If you fancy the roar and a little better throttle response get an induction kit / cone filter,
And if you really want to splash the cash you could get something a little upmarket like a BMC CDA, Although I can't vouch for the sound or performance with these, but many people on here rate them highly
Induction kits don't add power. They add noise, and some more repsonse, but not power.
Panel filters add response and a teeny bit of power, but no more noise. My K&N panel filter added some nice response lower down the rev ranges.
Aftermarket airboxes like the BMC CDA seem to be quite good power wise, but on the downside they are quite expensive and apparantly you lose a few torques as a sacrifice, which in such a small engined car i wouldn't really want to lose...
get yourself a K&N panel filter, get a K&N cold air hose and chop the airbox end of the standard intake off, put it back on the airbox and wedged and bondo the hose on. also i took my airbox lid off and removed the resonator box from in there. thought it was shite to start with but with the FULL exhaust swap and a ghetto tune up on the timing it runs awesome.
tbh the induction kit isn't really going to do much on a 1.4... at all, except add noise. the biggest restriction in the 1.4 is the ports & valves in the head, along with the teeny weeny throttle body and the exhaust manifold. first port of call for me if I were tuning a 1.4 again would be the exhaust manifold. the one I had on my old 1.4 (which Tommo now has on his) gave a VERY noticeable improvement in bottom end torque, along with making the engine feel less restricted at higher RPM (basically it would run out of any real puff at 6000RPM rather than 5000RPM). I also had a decat in there which had a similar effect, but to a lesser extent than the manifold (be warned, my car failed its MOT without the precat that the manifold replaces, despite having the main cat in place).
the short version is don't bother with an induction kit until you've done a few other things first. until then you're much better off with the better filtered air going into the engine.
agreed i put a filter on, improves throttle response, thats about it. The noticeable gain came from the manifold, used to watch my mates zetec s drive away with ease, not anymore and considering the weight difference thats impressive!