my question is ... should I gut the cat...get a pipe and weld it there instead or do they sell a test pipe that fits and bolts right up???

 

yes many companies sell a "cat replacement" presilencer, directly replaces the cat
www.racingbeat.com for example

 

Well if you gut the cat it will sound weird. When it backfires it will sound like it is happening in the cat. I would recommend measuring the cat, (I believe when I did it it was 17" or 17.5") then going to an exhaust shop and getting two flanges welded on the ends like the ones the cat has on it. Or you could spend like $75 bucks and get one from Corksport.

 

If its s4 NA don't forget about the split air pipe for activating your 5&6 ports. If you weld in a straight pipe you will lose this functionality and performance will suffer. I have one of the bonez high flow cats and it works pretty well, flows much better than the stock ones. I sometimes wish i had just gutted my stock cats, i havent heard of them sounding wierd on a rx7 but i've never tried it. I know on hondas it works very well cause my friend did it and it sounds a lot better than hondas with straight pipes, and opened exhaust flow right up.

I'd say its worth a shot to try gutting yours. The hardest part is getting the old old bolts out and once you do that, taking it on and off is a cinch. The worst thing that can happen is you are careless and break your factory cats causing an exhaust leak at which point you'll have to replace it. I'd definately invest in some new gaskets for whatever you do, you can always re-use them on a different set up if you dont like how it works.