If you decide to weld it, make sure that the arc welding fumes do NOT pass through the Cat, that will kill it stone dead!!! (any Pussy!)

Its best to have a bit of low pressure clean air passing through it to make sure.

If you don't want to replace the damaged exhaust pipe, take a section of exhaust pipe repair tubing long enough to extend past well past the damaged portion, split it and fit it over the damaged section. Weld the split and the two ends to the existing pipe using a MIG or TIG welder.

I've seen this done by an exhaust workshop but using muffler putty to seal the split tube and fastened with U bolts. Seemed to work okay for a couple of years. I think it sealed the flexible coupling on a 1973 Austin Kimberly.

You can try a junk yard replacement for the pipe and muffler. The junk yards aren't allowed to sell a used Catalytic converter. You can buy a section of pipe at a muffler shop or parts store use a 1/2 inch wide ring cut off a piece of slightly smaller pipe from the muffler shop put this under the two pieces as backing for the weld joint. Use a mig welder and weld all the way around the pipe.

I don't know your skill level but a trip to a good muffler shop is what I would advise.

Any decent muffler shop that does 'custom exhausts' will not have any difficulty in repairing the crack/hole.

bett4haze check this out,

Go to http://www.walkerexhaust.com/defaultEN.asp this is the home page for Walker exhaust systems. From here you can easily drill down to your Infinity parts.

At Rock Auto.com (http://www.rockauto.com/catalog/raframecatalog.php) you can purchase an entire OEM style Walker cat back exhaust system for less than $300.00 (plus shipping and applicable taxes). My guess is 2-3 hours of labor if you are a handy DIY type and this problem will be solved.

I truly support individual resourcefulness and have personally pushed the creative engineering envelope to several painful conclusions. Some things just work better out of the box.

Personal disclaimer I have used Walker exhaust components for over thirty years and Rock Auto has become one of my personal favorites for internet auto parts. They also have outstanding customer service.

JB weld is a heat proof epoxy that resists oil and is completely maliable however you must clean the exterior of the connection point with solvent making sure that it is free from dirt an oil residue before you apply the epoxy

If I sold new exhaust parts, I might tell you that you need to buy a new part. If I was a welder, I might never tell you that you need to buy a new piece of steel. I believe you need a second opinion. If your Infinity was located in an area of the world where there was no replacement parts I am sure repairing your part would be done. Another consideration is how difficult is it going to be to get the pipe welded. If it is going to require removing the part anyway, is it worth repairing it? Will the welding bill equal the price of a new part?