It's standard practice to run a crossover for improved performance, doesn't a cat do the same--if big enough??
I guess the cat back 'dulies' are just for looks
Straighten me out!

 

I have never been a fan of Cat's.. Pending on your setup. I completely removed it.. Plus, I am running a 4" exhaust and unless I want to run a truck convertor which won't fit under the car, It was just easier to remove it.

 

TRUE, but I ned to pass Calif SMOG.
Seems I've seen serious V8 race cars running 8>2>1 exhausts

 

2 pipes will allow more airflow than one..

 

---so I'll run two 1" pipes instead of one 3.5" one, does thaat work in MN??--it doesn't here in Ca.

 

yeah.. that's exactly what i meant. you must be a mind reader.

a pair of 2.5" pipes will flow more air than a single 3" pipe- if you have something that needs more flow than a 3" pipe can support.. GN guys claim to see a noticeable differences in spool up and trap speeds between dual 2.5" pipes and dual 3" pipes after a single 3" cat, but that could also just be them subconsciously justifying that $500 exhaust system they just bought..

 

Haven't I seen big money race cars using a final single pipe? As I recall Kastner the British Triumph guru used a 6>2>1 system in his internatioonal champion cars.
I'll try and get an answer from Dr. Dave Vizard who has several books about how to get the big HP from engines. He also dragraces etc.
Changes to the exhaust historically have much less effect than the input end having to deal with only the 14.7 PSI pressure pushing air/fuel in as opposed to the hundreds of pounds shoving the exhaust out.
Somewhere there will a comparison about such things.