I didn't even attempt to get those two pieces apart...much too frustrating! I just spliced in an 18 inch piece in the space between the cat pipe and muffler. Saves a lot of time and cursing!

 

Map gas is basically oxy accel. I'll prolly just use a saws all

 

MAPP gas is stabilized acetylene. Not quite as hot as acetylene but much hotter than propane.

I tried a sawzall, but not really worth it. That pipe is damn tough.

HeyYou, I didn't know you could heat that pipe up and slip it out. Usually I just cut them out with a torch and then have someone with a MIG weld the new one in.

 

Take a chizle or a flat head screw driver and gently tap it betweened the slipped pipes. Flair out the end of the intermidiate pipe tiny bits at a time all the way around the whole pipe until you can work out the end of the cat. You can still get a perfect seal with an exhaust clamp once the new cat is in. I did this and it worked like a charm.
If your intermidiate pipe is suuuuper rusty and old this could be a riskey, you just don't want to get crazy and bend the crap outa the end your intermidiate pipe or chip and crack pieces off if its really rusty.

 

Learned that trick working on old hot rods..... Even pipes that were clamped together (and thus, somewhat deformed by the clamp) will come apart with a bit of convincing.

 

Ive used mapp gas to heat and bend rebar. It gets red hot, just takes a while

also, ive cut many a pipe with a sawzall. just need a bimetal blade