Use heat, cheater bar, put the other bolt back in and support the cat. or borrow a air compressor and impact gun. Let us know what happened.

 

Put a Pipe on the rachet, that should work.... hopefully.

 

you need a breaker bar

 

try tightening it first, you'd be surprised how many times I've been able to break a stubborn bolt by trying to turn it clockwise and then counterclockwise.

 

well i got it off and installed my RS-R exhaust... the wd-40 didnt work so i just sat on the floor for an hour kicking the damn ratchet... it kinda messed up the nut so i just hammered the ratchet back on so it jammed and kept kicking it more for another hour and i just came off...im like wtf....ehhh thanks for your input guys! the exhaust is wonderful

 

I use a hollow metal tube that slips over my ratchet that's about 18" long as a breaker bar, works all the time.

 

Go to a hardware store and pick up an electric impact wrench. Mine has saved me a lot of time and anger. I got mine from harbor freight

 

It's a pain in the ***, ain't it. I spent like 6 hrs to take off the cat. (That was because it's winter and it's like 0 degree in my garage)
At one point i got so **** off, it's so damn hard to take off any bolts, they are all rusted. The last bolt took me the longest time to take off. In the end, I use a jack to "staple" the cat. (don't know if you know what i mean) Then i just unscrew it the hard way.