here's what I noticed with a similar car:
I've got a mild build: 7-rib bastard large port, 10.3:1 0.5mm (first oversize pistons), .8mm TRD headgasket, new valves (stock size), stock cams, and stock ECU. Stock exhaust manifold and downpipe.
Originally, the car had a 2.25" cat, and a straight-through under-axle exhaust, terminating with a huge fartcan. it was loud and obnoxious, and I didn't like how low it hung.
So, I made my own system, going OVER the axle: cherry bomb "turbo" muffler in the back, cherry bomb glasspack in the middle for a resonator, and a carsound (magnaflow) universal cat. Everything was 2" inlet and outlet, and I used 2"mandrel bends, as thick as I could find them, which I believe was 16 gauge. I wanted 14, but that was hard to come by.
No more low hanging fart can, and the car is now MUCH quieter. Funny thing is, the car seems to have a LOT more grunt pulling through the gears. I can definitely feel the power coming in a lot lower in the rpm range. It used to be kind of peaky: weak until about 5k, then it would be really good to about 6.6k, then it would run out of power again.
I had it dynoed after I put on the exhaust, but nothing beforehand, so it's really kind of a useless comparison.
But, those are my observations with exhaust and the 4AGE engine. I'll be putting in new cams and a header shortly, so we'll see what happens then. I think with your engine, 2.25" would be defintely better than 2", but my gut leads me to believe that 2.5" is too big for the engine, and the scarcity of torque in it will be amplified by such a large pipe.
--sarge
---** To be in compliance with the Anarchy **---
Jorden R. Kleier
Baraboo, Wisconsin, USA
1990 Mazdog Protege 4WD
1973
