Ok so removing the stock cat...

Originally Posted by Motordyne

Find a EXTRA LARGE 1/2" breaker bar (like used for tightening lug nuts) and use a 3 foot long 1/2" extension and connect it to a 1/2' impact socket (14mm).

Use only 1/2" socket tools and get ready for some serious torque!!!

PB Blast it, put on leather gloves, one hand on the bar pivot point, the other hand at the far end of the breaker bar. Brace yourself with a low/stable stance and crank that bitch until the bolt yields or snaps off. BAM!... Problem solved.

Unfortunately there is no way around it. That's why its called Demon Bolt.

Originally Posted by vividracing

This sounds exactly like how a proper man would handle the demon bolts! The only things I can add is that you may want to let some PB Blaster soak for a while and a pipe fitted to the end of the breaker bar will give you more leverage if you need it.