does it make any difference in the xu10j2c 2.0 8v?? replacing original airfilter with k&N air filter, also does replacing standard spark plug wires with a splitfire set give a better throttle response from the engine???

Don't expect any noticeable increase in power from a K&N air filter, the main advantage is that you can clean and re-oil them. Same with Splitfire HT leads, the standard leads are fine. Some after market leads are crap because they don't fit that well.

And the noise...