For cutting my muffler pipes, what is the best thing to use.

My cat is rusted together and I'm just going to replace it with a straight pipe.

So what's the quickest tool.

Or else I'll be at it with a hack saw for a while...

 

I've been using a sawsall for about 5 years to do exaust systems, will take about 15 seconds to cut the pipe

 

Lisle (and probably others) make a cut off tool; it's got four cutting wheels on it. You put it around the pipe, tighten it, and swing the tool back and forth about 90 degrees. When the tool gets loose, you tighten it again, and keep swinging. Eventually the wheels cut all the way through. Be careful when cutting a factory y-pipe! It's double-walled and the tool won't make it through to the second wall.

And there's nothing wrong with a hacksaw! Just wear gloves so you can saw really fast and not worry about slicing your hand on the underside of the car.

What piece is rusted? The back of the cat (two bolts), or where the cat enters the y-pipe? If it's the front, and you're destroying the cat anyway, then just hack at the front flange of the cat. Hammer a large screwdriver between the end of the y-pipe and the cat input pipe. Eventually you'll bend the cat input pipe enough to slide the cat off. Then, use an "exhaust pipe expander" to restore the end of the y-pipe to a round shape. I bought my expander from Pep Boys for $20, and they probably rent 'em. If not, you could always work the y-pipe end back into a circle with a little hammer... it'd take forever, though. It cost me $180 for my replacement y-pipe back in '96...

 

Well I've been trying everthing I could think of.

The bolts and flanges are all rusted together.