I was wondering what the most popular and cheapest conversion for Fieros are. I have an 84 with the 2.5 and I want to put a modern engine in it. Like a DOHC 24v aluminum motor in it. I was thinking of a 1.6l motor out of a Geo Prizm(it's actually a Suzuki motor). Another thing is where can I get performance parts for the 2.5?

Why a Geo 1.6 and not a B & S. The cheapest conversion would to go with another iron duke. Or if you want a simple conversion go with the wide range of V6 engines you can put in.

from 24valve v-6 to like 8? valve 4? cylinder... to performance parts for a 2.5? Im confused what are you trying to accomplish?

There are no easy engine conversions in an '84. I'm in the midst of a Quad 4 swap and it's a bunch of work. Any V-6 or V-8 is more difficult.