I am doing my research for upgrading my exhaust (my 1990 still has the original exhaust). I believe the 3 inch cat back system won't fit because I have original 1.6 axels, is that correct? I hope i'm wrong.
If so, will the the Enthuza 2.75 inch fit?
Thanks.

3" will fit, it does on my car anyway.

The little "ears" on my 1.6 axles used to hit the exhaust slightly if I was accelerating hard AND going uphill, but they've worn enough of an indentation into the pipe that it never happens anymore. YMMV

I have had this question a few times. I can make a "ovalized" section to the 3" tube for more clearance of the tabs on the 1.6 axles. Jason.

You have a 1.6 and low boost. Unless you plan on going over 250whp I'd just get a 2.5 exhaust.
I know most (if not all) on here are strong believers of 3", but the 2.5 will be almost as good, and a huge improvement over your stock exhaust. And by that I mean HUGE.

BIG +1

Being in your shoes...don't worry about it. Go 2.5" and be happy with the big kick in the ***.

I should have mentioned that I plan to ad an intercooler and get to 8psi, or in other words get as much as I reasonably can out of my begi-s setup. But that will still put me way under 225 hp.
So for my plan, will those cheap exhausts on ebay be good enough for what I am trying to accomplish?

Again thanks, I am learning.

The begi-s can go way higher than 8psi just so you know. (Not on band aids of course)
And 8psi will put you at around 190-200 with a decent tune (I'm assuming you don't use band aids).

if the ebay exhausts you're referring to are 2.5 EVERYWHERE (meaning no bottlenecks or tapers) and are fairly free flowing you should be good to go.