I know this is an old thread, but it was here, no sense in starting a new one. I bought the NAPA professional series tailpipe expander, it was about $40. It was made by KD but in Taiwan. I thought I would try it out. It broke a small piece of one of the fingers off with my 3/8" ratchet. Then I tried the impact and that destroyed what was left of it. It actually took the threads out of the adjustment nut. I think it broke all but two fingers. I slit the pipe before trying this tool! I did not use heat due to the o rings being rubber. I would like to say that these type of expanders should only be used to round the pipe back to existing size. I did purchase a Lisle tailpipe stretching set for $189.
http://www.tooltopia.com/lisle-17350.aspx
That should let me change the ID to fit the OD of the next section. I will report back on the new tool when it comes in.
Here is another thread that discusses the tool I am getting. As well as other "expanders".
http://www.garagejournal.com/forum/showthread.php?t=25912&highlight=tailpipe+expander