I just put the American Thunder kit on my 68. I didn't get any resonance, and the tail pipes look really cool too, as opposed to coming straight out under the bumper. I think it's actually louder than the 2 1/4 inch exhaust I had on it with cheap turbo mufflers though. Sounds awesome!
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68 Coupe, 350 4-speed
Jim's Camaro Corner
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68 Coupe, 350 4-speed
Jim's Camaro Corner