I have to disagree here a little bit. Any muffler before the turbo is going to hurt performance some. Some mufflers more then others. a muffler will have some restriction depending on what type it is, which may slightly increased pressure/heat, but a muffler will also act as a radiator dispersing a lot of heat in its self. Inlet temp and exhaust volume will aways be higher then out let temp and volume. How much will depend on the type and size of the muffler, as a larger, more restrictive muffler will radiate more of the heat then a smaller strait though muffler. That's just physics.

 

I wanted to mount a turbo in place of the cats. How would that work? Both cats are under the passenger side seat. Will the turbo create more heat than the cats? What do you do about the o2 sensors?