I have the long case Dynomax mufflers on my automatic 69 GTO convertible. I used the Pypes 2 1/2" headpipes with stock logs and Waldron 2 1/4" tailpipes with resonators. It also has a H pipe. The car is very quiet at all speeds.
The Dynomax is one of the highest HP mufflers despite the very low db readings.
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