sportrak 1.6 engine upgrade????


Iv got a 93 sportrak 1.6elxi and was wondering if anyone has upgraded their engine to something with a bit more clout???? Ive done the usual mods like the K+N filter which has helped with the extra power a bit as well as changing the plugs and fresh oil also helped BUT...... as iv been reading the posts it would seem that theres not really much else i can do with this engine, i could change the Header pipes and put on a sport exhaust but id still be stuck with a 1.6.... so i was thinking.... "How feasible would it be to put a bigger engine in" And where would the donor come from? What do you guys/girls think?