Just re-did my exhaust and love the sound, but was just curious about some other options that I had previously thought about. I was wondering what is louder? the cat-bypass pipes with a muffler on (fabspeed makes some) or the muffler bypass pipes with the cats still on.
thanks

 

I haven't heard a cat bypass w/ mufflers still on w/these cars...but a friend has a c2s w/full muffler delete and I have the same on my gt3 and both are extremely loud.

I would say muffler bypass is louder, have heard cars other than 997 w/ cat delete and doesn't make as much of a diff.

 

It's been my impression, though I've not done any experimenting, that cats (stock, 200 cell, whatever) quiet the car more than the typical mufflers do.
I just installed a set of pipes behind my stock cats on my Ford GT - replacing the big muffler that spans the width of the car. So, huge muffler removed and pipes (Accufab) put in their place. It's quite a bit louder but not nearly as much as I thought it would be.
So, using the transitive (??) law of noise reduction for the OP, I'd say that on our cars (and other high-performance cars that need to minimize back pressure in their exhaust systems) the cats reduce noise more than the mufflers do.

 

I am here to tell you that cat delete is wicked loud.

dr