I've got a '70' 400 with 2.5 aluminum and three stage Flowmasters. Sounds nice for stock engine. I had two stage Flowmasters for a day and found it to be to loud for daily commute. Convertible hardware rattled.
But there sure was a greater response and hp with the two stage from stock mufflers. And there was a noticeable difference between three stage vs. two stage, two gave more power.
This was very clear for me to recognize since I had ran with stock mufflers for 17 years. I am sure others will have more input on different brands and post.
I like mine for now but will change when tired. Look into a type that gives the performance and sound that you want. My Flowmaster three chamber's sound deep with a hint of tin.
Tilster
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