from wat i saw my fren did, and common sense...but tis might be 'kampung style' la, maybe there is other way tat is better than tis..
1.buy a manila card, thick one, or else buy 2, compile it together to make it even more thicker..buy a spray..
2.measure the size, use a pensil to draw the wording ex : HKS or watsoever...
3.cut the words with a scissors...
4.use tape to hold the manila card wit your intercooler so tat it won't not move during spraying process..(make sure it is tight/fit/firm enough)
5.spraying skills (i don't know how to spray so u might need to consult other ppl how to spray, regarding on how far the range,etc etc)
6.after spraying, try to leave it til it's dry then take out the manila card..there u go wit a kampung style spraying method :D