Like Tom said, Dynomax makes some nice mufflers and if you can get a smoking deal they are certainly worth running.
I've always had great luck with Magnaflow. Here's one reason they flow so well. An almost straight through design.
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"A ship in port is safe, but that's not what ships are built for."
See Bad Penny run the cones:
https://www.youtube.com/watch?v=8GUPPIX-92U
1971 Chevelle Wagon - Roadster Shop Chassis ProCharged Shafiroff LS and lots of yada yada
1968 Camaro - Project Track Rat - 440 RHS LS