In most states, hollowing out a catalytic converter is not only difficult, but also illegal. There is no good reason why you should need to hollow it out, and doing so can land you in a lot of legal trouble. The best solution is to keep the catalytic converter as it is and try and seek another solution to your problem. However, if you are determined to hollow out your catalytic converter, then there is a way that you can do so. Accept ahead of time that you may break your car, or cause running problems, and may find that a garage is unwilling to help you fix the problem if your catalytic converter is not working properly. This is a process you will have to do yourself, as no professional will take on the work.
Step 1 - Remove the Catalytic Converter
Remove the catalytic converter from under the car. It will be located by the exhaust, and is often attached to it, so you may be able to reach around and touch the cat, but you will not be able to remove it without lifting up the car. Get two floor jacks, and position them under your car so that the wheels are fully supported. Lift up the car, secure with jackstands and go underneath. Then, using your wrench, loosen the bolts which hold the cat in place, and gently draw it off of the exhaust as you remove the bolts.
Step 2 - Hollow it Out
You should now be able to hollow out your catalytic converter. Take the part to a workbench, and insert it into your vice, facing upwards so that you can see a honeycombed core. Wear respiratory protection. Take the crowbar and put it into the top of the converter. Using your hammer, gently tap the bar, and you will see the core begin to crumble. You should be able to reduce the honeycomb to a fine powder with a few strokes. Empty the catalytic converter, turn up the other way, and remove the core from the other side in the same manner. Continue until the core is completely gone.
Step 3 - Reinstall the Catalytic Converter
To reinstall, slide it back onto the exhaust, and push it into place. Take your bolts and screw them into place by hand; then, tighten them up using the wrench. Once the cat is in place, get out from under the car, and remove the floor jacks. You will be left with a large amount of powder, which contains platinum, and can be recycled or sold for cash if you need to. Your catalytic converter will now run without the core, but will not do the job it was designed for..