will I benefit from putting on an old cat converter and increasing pipe size from glass pac on out to 2.5"? got no cat and 2" pipe all the way now.got all the stuff sitting around the yard.

I just put on pacesetter headers and a 2.5 inch pipe to the cat, another 2.5" pipe to a muffler and then a 2.25" tailpipe. It made a bit of a difference but should be more helpful as a modify the vehicle more later. (such as a performance cylinder head and perhaps a larger throttle body). I have heard that opening the exhaust has more effect on higher RPMs but doesnt do much for low RPMs. Thats about all I know on this subject.

These things are pretty well tuned to the stock 2-1/4" exhaust. Open it up too much, and you'll lose the backpressure and some oomph as Gregg mentions.

Would be okay I'm thinkin', if $$ is an issue for now; can refit later.

yes money would be a concern thats why I want to use the parts off the old parts truck ,I wonder if it will run better with a cat than without( and cleaner).I have also heard of using 2.5 pipe from the muffler back.My truck runs fine now,I would not go out and buy this stuff but Ive got it on the parts truck in the yard.

mine is stepped from 2" DP to 2.5" cat and muffler... and it works great, mine is a v6 though.

i gotta agree with greg_canada. im runnin 2.5 off the headers, to a hi-flow, and a glass pack muffler with 2.5 in tubing. really opened up my truck.

Yes, a cat will help your rig run better and cleaner. Since these engines aren't race engines they aren't designed to work with an open exhaust, they work best with the exhaust components that came with them. They need some amounts of back pressure, a cat will add just enough as long as you don't open up the exhaust to much. The old cat should work fine providing you can still see some amount of light through it

You could increase the tube to 2.5" if you have free tube laying around, though 2.25" tubing IMO is better, inside diameter that is. I increased the exhaust on my '91 22re from stock to 2.5"I/D from the cat back and hated it, no low end torque and maintaining 55 on the highway while climbing hills was impossible. I dropped the tube down to 2.25" I/D and it seems to perform better. My tubing was also a straight shot, no bends at all, so the usual bends in the tube might make a difference with the larger tube.