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I run duals on my 79 with cats, no muffler. I love the sound. I thought I'd do the same on my 91 sub, but it has larger diameter pipes, i removed the muffler, and ran w/ cat only....oh my, that puppy was so loud. But the sub was so much louder w/ fatter pipes. I had to go back and put a muffler on it. I still run my 79 383 without a muffler, just cats-sounds awesome.