I run a magnaflow in front of my corsa and a magnaflow behind it. Over time the magnaflows always burn out all their packing. I've done this to 4 of them. I know it's do to the exhaust temperature and velocity.

Has anyone had a straight through muffler with packing hold up to forced induction?

 

My thinking is you are dealing with excessive heat and pressure in your cat back with only a 3" pipe. I'd bet 10PSI at your shift points. The positive pressure is only creating more heat.

Open it up to a 3.5" and my guess is the problem goes away. You will reduce heat and velocity. If you tested backpressure it would surprise you.

 

Vortec- do you run any additional muffler with your corsa?

 

Open that exhaust up, I have a thread on exhaust back pressure. Mine was high with a single 3" ( actually 2.8" based on pipe ID) I went to single 4"

 

I do but mine is a corsa for a diesel, so its a 4" pipe. I have a borla muffler in line.