I run a set of the long 2.5" 17748 or 17749 (Hemi super turbo) on my '64Dog. At first it felt like they were too quiet, but after a few months they turned just right. I make a lot of long trips and they don't drone. I've had admiring comments from grownup hot rodders. I like them so much I put one on my '75 Mercedes 280! Quieter than the old Corvair turbo muffler but has a really nice sound.
